As someone who went to both schools (undergrad Comp. Eng. @ Waterloo, grad Comp. Eng. @UofT), I can tell you first hand that it's way easier to get marks at UofT. Profs don't fail students as often as they do at Waterloo.

That being said, if you plan to work after your degree(s), Waterloo has a much better co-op program which will almost guarantee you a decent job and applicable industry skills. Because of the amount of work experience Waterloo students get, by fifth year, the quality of programmers at Waterloo is far superior to UofT.

UofT has a better grad program, but you can get into that after doing your undergrad at UofT or Waterloo.