There have been physics students in co-op working at NASA and CERN as well. I am fairly certain both of those students found those opportunities on their own, rather than through the co-op office. The office posts some pretty great opportunities as well, such as the Canadian Space Agency.
As was already mentioned, getting into the program is based on grades, an application, and an interview. Physics is a fairly small program, and the number of people who choose to do co-op is even smaller. If you are interested and show it by putting effort into your application, you should have no problems getting in