I just didn't sent any Cegep grades. No one asked, LSAC or schools. However, I did have 5 years of undergrad (instead of just 3), as well as 6 of grad. That might have signified the complete irrelevance of what I did in Cegep to them. In any case, I would not volunteer them and would just submit what is asked for: undergraduate grades. Cegep is not college or university.
As for Ontario schools, I have no clue. Best of luck.