... you can't fly a US registered aircraft in Canadian airspace without a US license ...
I am not aware of all the issues associated with importing an aircraft, but I don't believe the above statement is correct. FAR 61 has a specific exclusion which covers operation outside the US:
61.3 Requirement for certificates, ratings, and authorizations.
(a) Pilot certificate. A person may not act as pilot in command or in any other capacity as a required pilot flight crewmember of a civil aircraft of U.S. registry, unless that person?
(1) Has a valid pilot certificate or special purpose pilot authorization issued under this part in that person's physical possession or readily accessible in the aircraft when exercising the privileges of that pilot certificate or authorization. However, when the aircraft is operated within a foreign country, a current pilot license issued by the country in which the aircraft is operated may be used; and ...
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The wording is a bit tough to read if you aren't a lawyer, but Canadian CAR 401.04 (a) says that you can fly a foreign aircraft in Canada using your Canadian license:
401.04 No person shall act as a flight crew member or exercise the privileges of a flight crew licence in Canada in an aircraft registered in a contracting state other than Canada, unless the person holds, and can produce while so acting or while exercising such privileges,
(a) a flight crew permit or licence issued under this Subpart; or
(b) a flight crew licence, or a document equivalent to a foreign licence validation certificate, that is issued under the laws of the contracting state.