This topic has come up before. What would happen to passengers on a domestic flight if that flight had to divert to a foreign airport. Fog in Halifax ( CYHZ ) forces a diversion, it looks like the first choice was Bangor ( KBRG ) than Moncton ( CYQM ) was chosen as an alternate.
There are no requirements for passports for domestic travel within Canada, but there are passport requirements to travel from Canada to the U.S.
Could there be consequences for someone not ’ prepared ’ to enter the U.S. or would the flight just park on an apron and wait for conditions to abate at the original destination.