An example of something I checked, before ordering from .com:
https://www.amazon.com/gp/product/B07ZZ3W2H8/
versus:
https://www.amazon.ca/gp/product/B07ZZ3W2H8/
I've occasionally seen such listings at 10x, but commonly 2x-3x is common (as with this listing, after exchange). You also lose all 'shipped by Amazon' protections, and if the listing at .ca was FBA, you'd have free shipping in .ca.
(As a note for .com / US users, Prime membership on .ca does not give any discount when shipping to Canada from .com, as Prime membership is restricted to the .XX property which you buy it on. EG, .ca in my case.
Nor does buying a .com prime membership help, for that only gives speed/discounts/free shipping for US addresses.
When I travel to the US for the winter, I basically have to axe my .ca prime membership, and buy a .com membership. So as a result, I don't buy yearly memberships. And when I travel to/from, I cancel .ca early, and .com early, upon return.
It's not like I order a lot of stuff 3 days before leaving, or while traveling, or the second I arrive.
A result of all this is that Amazon loses out on sometimes 4 months of Prime membership, which they would have if it just worked everywhere.