Welp, it does make sense since regulation can be different in each province though it is concerning that they did not update their tos to imply exceptions. My best guess would be either they were too lazy to update their fine prints or they're secretly passing folks in their prohibited country list.
Looks like you're not the only canadian who has passed kyc, see:
https://www.reddit.com/r/MEXC_official/s/DS2a9DJO9MYa. I thought about both of those things. I'm going to keep inquiring into the situation and see exactly what they are doing and try to figure out how the terms of use reflects what they are doing.