Characterizing students who study here and then gain permanent residence as "back door" immigrants is probably a little bit much, since it is explicit Canadian government policy to attract people permanently to Canada exactly by that route. But I agree it helps to explain some of the increased popularity, since Canada has only recently developed those immigration programs. I also think there are a lot of other positive spinoffs, some probably hard to quantify, from funding international graduate students to be here. The skill level of undergraduate students is a bit of an issue, but the same can be said of Canadian students. And the system is designed so that you get that less in graduate school, and also employers select against people who have not done enough work to develop their skills out, no?