He will only need an antigen test to fly to the States but PCR within 72 hours of arriving in Canada. That, too, is covered. Just need to make sure I can get into Buffalo and cross him back to the border within that 72 hour period of his PCR test in Mexico.
Sure - I just don't know that stuff. I don't even know what applies to you crossing and coming back. Just that he should be fine with his expired pr card and other docs you have.