Both American and Canadian regulations do not allow you to fly in Canadian Airspace with BasicMed.
Overflights through Canadian airspace with BasicMed are also not allowed, regardless of who controls the airspace.
FAA Regulations
Section 61.113(i)(2)(iii) requires that the flight, including each portion of that flight, is not carried out outside the United States, unless authorized by the country in which the flight is conducted. Title 14 CFR part 1, § 1.1 defines the United States as the States, the District of Columbia, Puerto Rico, and the possessions, including the territorial waters, and the airspace of those areas. Thus, a pilot operating in the United States, as defined in § 1.1, may elect to use BasicMed. Airmen certificated by the FAA are represented to the International Civil Aviation Organization (ICAO) as compliant with ICAO standards for private pilots, among other requirements. As BasicMed standards divert from ICAO requirements, flights must be geographically limited to operations within the United States, unless specifically authorized by the country in which the flight
Canadian Aviation Regulations
404.03 (1) No person shall exercise or attempt to exercise the privileges of a permit, licence or rating unless the person holds a valid medical certificate of a category that is appropriate for that permit, licence or rating, as specified in section 404.10.
(U.S. recreational pilot certificates and sport pilot certificates are not recognized in Canada)
