Originally Posted by DOC_Ma
There is one but fairly low. The real cut off depends on the school and most importantly the department. It's the hardest to get at biology due to all premeds but much easier at earth sciences and relatively easier at chem (at my school).
As a chem major I can second that it's the same at my school. They also just seem to offer more of them to chemistry, despite our smaller size. Quick note about NSERC: to hold an NSERC USRA, I believe you need to work with a professor who has a NSERC grant of some kind. If you want to do research with someone who doesn't, that could be an issue, but there are ways around it. This is a bigger deal at smaller schools.