If you read Samuel Huntington's "Who are we", you might com out with different conclusions. The Americans make it clear that there are second class immigrants - Muslims, Hispanics, Chinese, etc whose loyalty will always be questioned. That is the reason a lot of Jews volunteer in a kibbutz, or have dual citizenship. 

American liberals have held up Canada as a perfect example of immigration. There are no major parties here that are anti-immigrant. One day, in a few decades, Hispanic majority Texas may secede. Whereas large scale immigration will ensure that Quebec never can. Even in 1995, it was the immigrant vote that swung the referendum.