Amazon opened the Toronto office back in 2011 because there was demand- Canadians who didn't want to live in America anymore- often because of family, friends back home or because they wanted to have kids and not raise them as Americans, culturally.
It started with less than 10 people, plus the hiring they were able to do locally. It's now an office of over 300 people, maybe 100 of which transferred from Seattle. And the transfers back haven't slowed much- lots of folks simply want to come back home after a few years.
Lots of room here to grow. If Trump wins, I expect we'll need it.