<p>If you are in a thesis based graduate degree (ie. most natural science degree), a large part of getting into graduate schools is finding a supervisor who can fund you. In my experience the supervisors tend to choose the best available applicant, regardless of nationality. I also now tons of UofToronto graduates now in US grad schools (including one at Stanford), so if there is a barrier for internationals getting into good US grad schools, it certainly is one that can be overcome.</p>