I'm unfamiliar with how the rest of the world works when it comes to immigration and entrepreneurship. Is it difficult to start a startup in Canada or London if you aren't already Canadian or a resident of the UK?
I think you can get your permanent resident status in both countries in < 2 years, whereas in the US it could take anywhere from 2-8 years depending on where you're from (really bad if you're Indian/Chinese) and what phase the moon is in :)