While I don't know the particulars of how the Political Science department is viewed abroad, I'm inclined to say that University of Toronto's reputation is strong enough to serve you well in an American job market. If you were looking at a different school in Canada, my advice would probably be different, and I had to decline one offer for just that reason. University of Toronto is an internationally recognized school, though. (You'll find most people in your cohort will know what place UofT has in the global rankings.) I got a Master's degree from them, and I have found that it opens a lot of doors. Aside from that, the experience was wonderful! I would have loved to stay and do my Ph.D. there.