United has huge point of sale pricing differences and I assume Air Canada does something similar as well.
I book a lot of United flights directly on United website. Usually round-trip YYZ-DEN. In my United profile, I have 2 addresses listed, my Canadian address and an address at a friend that lives in the US. I have seen price differences of a few hundreds of dollars cheaper if at the last step of the booking when I use my US address over the Canadian address (factoring fx conversion).

Then I've seen the opposite happen when I booked a YYZ-SFO-TPE where the US price was way higher than the price with my Canadian address.

Morale of the story is I tend to check AC Canada, AC US, United Canada and United US for trans-border and international flights.