As a U of T alumnus about to do postgraduate study in London next year, I can tell you that a good 2:1 will be okay for a Poli Sci. Ph.D. A 1st would be better, of course, but whatever. Professors will look real hard at your research proposal so write a real good one. Good references help, of course.
As for its fame, within Canada, most people would think UToronto to be more prestigious than McGill and I was surprised when I began to realize that abroad that it wasn't the case. It isn't as popular with US students, which might be part of it.
That said, I'm not sure the amount of people we send to Harvard is any indication of quality (good or bad). It depends on who applies, right? I know that at least one of the two Rhodes Scholars allocated to Ontario was from U of T. In the Poli Sci. department, actually.