That’s the catch, they are different marketplaces which play by different rules. As far as .CA is concerned, your US trademark has no legal authority in Canada. I was shocked at this as well but it does make sense from a strictly legal point of view.
In no way am I defending Amazon on this. I’m just sharing what I found out in a similar situation. You’ll find CIPO much easier to deal with than the USPTO, they are just really slow. I’ll give you a big hint, look at their application suggestions very closely. I can’t remember exactly what they call it, but it’s something like pre-approved product categories for your trademark. If you can use one of their pre-approved categories it will save a long, long time on your application.
Good Luck,
TJB