Couple thoughts:

- Remember that cabotage is not a business rule or policy, it's a law.
- Irregular ops on a domestic itinerary with the US are highly unlikely to trigger regulatory exceptions to cabotage, even significant force majeure events, just because they happen to be near a country border.
- Getting two tickets issued with a short connection time might create uncomfortable questions with Canadian immigration for the passenger as to how this was ticketed and whether it should have been at all.
- Airline status should be irrelevant here.