I think a few important points haven’t been mentioned.
US colleges offer career services and alumni networks. I have known a couple of grads of non-Oxbridge UK universities who had trouble “launching” in the US. They loved their experience in the UK, but found that their colleges were largely unknown to American employers. They had trouble getting summer jobs in the US because UK summer vacation is different and shorter than those of most US colleges. (The UK schools have longer vacations at other times of the year.) Like the US, the UK limits the number of hours non-citizens can work. My understanding is that it makes it difficult for US students (with only American citizenship) to get substantive summer work in the UK. So, new American grads of UK schools often have less work experience than American grads of US schools, a real disadvantage in getting hired. Except for Oxbridge, which have made a concentrated effort to beef up their alumni networks in the US, the UK schools don’t offer the kind of alumni networks that help launch a career. Unless things have changed in the last few years, it’s rare for US companies to conduct on-campus interviews at UK schools.
One of the Americans I know gave up after a couple of years and moved back to the UK because she couldn’t get a good job in the US and could get one in the UK. She’s a grad of the University of East Anglia, which is actually world renowned in her field, but just wasn’t recognized by most US employers.
My understanding is that there are fewer such problems studying at Canadian schools.