There aren't many grad students at Waterloo (only about 3000). Waterloo is currently planning to triple the grad student body, but that won't materialize in the close future. I can't say anything about Queens, though I know someone who is a physics grad student there, a of latest news at least (he used to come on this forum by the alias of 'Data', but he haven't seen him active in a while). I can try to put you in touch with him, P.M. me if you are interested. Otherwise, have you gotten offers or are you simply pondering over the question? If the latter, have you considered UofT? Their grad studies are the strongest in the country.
I didn't look outside of Canada, perhaps for my PhD, after visiting the groups and the campus I decided on Queens, they seem to have a very active university in general, and the grad students I spoke to in the group I am joining seem very happy to be there.