Well, I'd suggest you apply and see what happens, I mean would you not consider dropping out of CEGEP for a while to see if your idea pans out? I believe that you could still get into an American University without finishing CEGEP(it's probably not the easiest way). Don't take my word for it bu they usually have a few path to get in and they have mature student options, and you do have a high school degree but with just a year less than US students. You should still be able to get in with that. As for McGill (great place ;p, I work there ;p) you can always finish CEGEP later and get in.

If you are convinced that you are ready to start a company I'd say apply now. You loose nothing.

Good luck.