If your brother decides to join, he will likely be sworn into the CF in late June, and head out to St Jean in mid august, as an Officer Cadet. The campus is located at the old CMR campus, and he can either take arts, or a general (science/engineering) program.
If your brother decides he doesn't want to continue after Prep Year, he can quit with no obligations at all. A few Quebeckers opted for that route on my course.
Here is the Prep Year website:
http://www.cfsj.forces.gc.ca/faculty/engraph/home_e.asp
Recruiting Centres should be helpful in filling out the correct forms, but just request ROTP Junior.
Cheers