And we have an expanding economy and a ridiculous amount of free space.

So not sure your thesis works.

Canada has a lot of land... but the majority of it is in the very cold northern part that people don't generally want to live in.

Also what do you mean with “lot of physical space”… May I remind you that this space is empty because, in both country, we have killed the locals.

I’m afraid you are considering Europe as “a lot of empty space”.

That's not at all what I was saying. I believe the US is wildly successful in integrating immigrants, since it is a nation of immigrants after all. Even the native population, which, despite what you said, was not entirely "killed". The indigenous population today owns a significant portion of land in the US and many tribes benefit significantly from using it or leasing it out (speaking from personal experience, the Agua Caliente and Apache tribes). Whether or not those tribes are "flourishing" is another fascinating story, but they certainly have the resources and potential.

USA has been successful at integrating the first kind, and the second one has just performed a nice illustration of their skills in New Orleans, like they do in my home country every year, and now every month, and one even said yesterday “We will rape all French people.”