Only Canadians may obtain licenses to provide the following commercial air services: 1) domestic air services; 2) scheduled international air services where those services have been reserved to Canadian carriers under air services agreements; 3) non-scheduled international air  services  where  those  services  have  been  reserved  to Canadian carriers under the Canada Transportation Act; and 4) speciality air services.
Since 2018, 'Canadians' in the Canada Transportation Act refers to Canadian citizens, permanent residents or companies incorporated in Canada that are controlled by Canadians and of which at least 51% of the voting interests are owned and controlled by Canadians. Additionally, a single foreigner may not own or control more than 25% of the voting interests in a Canadian air carrier, and foreign air carriers may not own more than 25% of the voting interest in a Canadian carrier.
Previously, the above commercial air services were reserved to Canadian citizens, permanent residents or companies incorporated in Canada that were controlled by Canadians and of which at least 75% of the voting interests are owned and controlled by Canadians. 
"PART II - Air Transportation
Interpretation and Application
Definitions
55 (1) In this Part, [...]
Canadian means
(a) a Canadian citizen or a permanent resident as defined in subsection 2(1) of the Immigration and Refugee Protection Act,
(b) a government in Canada or an agent or mandatary of such a government, or
(c) a corporation or entity that is incorporated or formed under the laws of Canada or a province, that is controlled in fact by Canadians and of which at least 51% of the voting interests are owned and controlled by Canadians and where
  (i) no more than 25% of the voting interests are owned directly or indirectly by any single non-Canadian, either individually or in affiliation with another person, and
  (ii) no more than 25% of the voting interests are owned directly or indirectly by one or more non-Canadians authorized to provide an air service in any jurisdiction, either individually or in affiliation with another person; (Canadien)
[...]
Licence for Domestic Service
Issue of licence
61 On application to the Agency and on payment of the specified fee, the Agency shall issue a licence to operate a domestic service to the applicant if
(a) the applicant establishes in the application to the satisfaction of the Agency that the applicant (i) is a Canadian, (ii) holds a Canadian aviation document in respect of the service to be provided under the licence, (iii) has the prescribed liability insurance coverage in respect of the service to be provided under the licence, and (iv) meets prescribed financial requirements; and
(b) the Agency is satisfied that the applicant has not contravened section 59 in respect of a domestic service within the preceding twelve months.
Qualification exemption
62 (1) Where the Minister considers it necessary or advisable in the public interest that a domestic licence be issued to a person who is not a Canadian, the Minister may, by order, on such terms and conditions as may be specified in the order, exempt the person from the application of subparagraph 61(a)(i) for the duration of the order.
[...]
Licence for Scheduled International Service
Issue of licence
69 (1) On application to the Agency and on payment of the specified fee, the Agency shall issue a licence to operate a scheduled international service to the applicant if
(a) the applicant establishes in the application to the satisfaction of the Agency that the applicant (i) is, pursuant to subsection (2) or (3), eligible to hold the licence, (ii) holds a Canadian aviation document in respect of the service to be provided under the licence, (iii) has the prescribed liability insurance coverage in respect of the service to be provided under the licence, and (iv) where the applicant is a Canadian, meets the prescribed financial requirements; and
(b) the Agency is satisfied that the applicant has not contravened section 59 in respect of the service to be provided under the licence within the preceding twelve months.
Eligibility of Canadians
(2) The Minister may, in writing, designate any Canadian as eligible to hold a scheduled international licence. That Canadian remains eligible while the designation remains in force.
Eligibility of non-Canadians
(3) A non-Canadian is eligible to hold a scheduled international licence if the non-Canadian
(a) has been designated by a foreign government or an agent of a foreign government to operate an air service under the terms of an agreement or arrangement between that government and the Government of Canada; and
(b) holds, in respect of the air service, a document issued by a foreign government or agent that, in respect of the service to be provided under the document, is equivalent to a scheduled international licence.
[...]
Licence for Non-scheduled International Service
Issue of licence
73 (1) Subject to any directions issued to the Agency under section 76, on application to the Agency and on payment of the specified fee, the Agency shall issue a licence to operate a non-scheduled international service to the applicant if
(a) the applicant establishes in the application to the satisfaction of the Agency that the applicant (i) is a Canadian, (ii) holds a Canadian aviation document in respect of the service to be provided under the licence, (iii) has the prescribed liability insurance coverage in respect of the service to be provided under the licence, and (iv) meets prescribed financial requirements; and
(b) the Agency is satisfied that the applicant has not contravened section 59 in respect of the service to be provided under the licence within the preceding twelve months.
Non-Canadian applicant
(2) Subject to any directions issued to the Agency under section 76, on application to the Agency and on payment of the specified fee, the Agency may issue a non-scheduled international licence to a non-Canadian applicant if the applicant establishes in the application to the satisfaction of the Agency that the applicant
(a) holds a document issued by the government of the applicant’s state or an agent of that government that, in respect of the service to be provided under the document, is equivalent to the non-scheduled international licence for which the application is being made; and
(b) meets the requirements of subparagraphs (1)(a)(ii) and (iii) and paragraph (1)(b).
[...]
Minister may issue directions
76 (1) Where the Minister determines that it is necessary or advisable to provide direction to the Agency in respect of the exercise of any of its powers or the performance of any of its duties or functions under this Part relating to international service,
(a) in the interest of the safety or security of international civil aviation,
(b) in connection with the implementation or administration of an international agreement, convention or arrangement respecting civil aviation to which Canada is a party,
(c) in the interest of international comity or reciprocity,
(d) for the purpose of enforcing Canada’s rights under an international agreement, convention or arrangement respecting civil aviation or responding to acts, policies or practices by a contracting party to any such agreement, convention or arrangement, or by an agency or citizen of such a party, that adversely affect or lead either directly or indirectly to adverse effects on Canadian international civil aviation services, or
(e) in connection with any other matter concerning international civil aviation as it affects the public interest,
the Minister may, subject to subsection (3), issue to the Agency directions that, notwithstanding any other provision of this Part, are binding on, and shall be complied with by, the Agency in the exercise of its powers or the performance of its duties or functions under this Part relating to international service.
Nature of directions
(2) Directions issued under subsection (1) may relate to
(a) persons or classes of persons to whom licences to operate an international service shall or shall not be issued;
(b) the terms and conditions of such licences, or their variation;
(c) the suspension or cancellation of such licences; and
(d) any other matter concerning international service that is not governed by or under the Aeronautics Act.[...]" (Canada Transportation Act (S.C. 1996, c. 10), last amended on 2020-06-10, Part II, Sections 55, 61, 62, 69, 73 and 76)
Canada Transportation Act (S.C. 1996, c. 10), last amended on 2020-06-10, Part II, Sections 55, 61, 62, 69, 73 and 76
[<a href="https://laws-lois.justice.gc.ca/eng/acts/C-10.4/index.html">Act</a>]