I disagree. Most other countries are pretty much mono-ethnic. Most western/first-world countries have some degree of representation from a variety of cultures, but none like the US. And I think the US is currently on the leading edge of progress in terms of cultural acceptance. I mean, consider how extremely taboo it is now to be seen as racist or insensitive (and this extends far beyond race.)
I don't think people from other countries, including Canada for sure, understand the environment in most major US cities, especially those near the coasts. I think if you turned Moscow into Los Angeles, you'd see how they really feel about minorities. It's easy to pretend to be open minded when your city is 90%+ one race, and/or when there are only a couple distinct ethnic groups largely confined to one area in a city.
I think people are roughly the same everywhere, and tolerance doesn't happen overnight. In the US, we've had a much greater degree of exposure to many races living side by side, and it took a long time and a lot of pain before things started to be more peaceful and truly equitable. And we've had a lot of carried over issues from the centuries past that other countries, with a more modern influx of foreign peoples, haven't had to deal with. When your country's main ethnic groups immigrated in the last few decades, yeah, it's going to be much smoother than if they came in 1950 or before.
But overall, I think people from other countries underestimate what it's like having a litany of foreign cultures around you all the time. Personally, I love it. I get to eat all their great food and learn new things about different people. But I am hard-pressed to believe that people from other countries, who aren't used to it and haven't grown up with it like I have, would see it that way. If you guys walked a mile in our shoes, you'd learn just how tolerant you really are and I think you'd be a little disappointed in yourselves and your countrymen. If America isn't the least racist country in the world, it's daaaaamn close to it.