Canada is like 70% white, around 10% East Asian, followed by around 6% East Indian/Pakistani, most of whom were educated professionals. As for them "returning to the mean", not sure what you are referring to. East Asians probably do better than Europeans on most academic tests so the mean is pretty high even if they were just average, which as I just pointed out they weren't when they immigrated.

Canada does have a small black population, maybe around 3 or 4%, and an almost non existent hispanic population oddly. It's also let in a fair number of Middle Easterners the last several years. Not sure what is confusing you really. The vast majority of Canadas population comes from nations that tend to do fairly well on academic and probably IQ tests, and Canada has a very good education system, certainly better than the US's.