I know students who got accepted to top universities in Canada after submitting their sophomore and junior year grades, before any senior year grades were available. I do not know whether they only looked at junior year grades, or if they considered both sophomore and junior year grades. It would not have mattered in our case (the grades were the same – senior year grades were also the same but came after the admission letter was already in hand). I used to know some other people who were asked for their mid term grades senior year. In most of those cases the students had known that they were close to the cutoff and had worked hard senior year and had good grades to send in.
I have consistently heard that freshman year grades do not matter at all assuming that you did not flunk out of high school.
I would say that admissions in Canada is much more predictable than in the US. If you have top grades, then you are in.
I know many people who went to Toronto or McGill or UBC. They have consistent said that these schools are large, academically challenging, and academically excellent.
There are however quite a few other very good universities in Canada. Most are large but there are also a small number of very good small universities (Canada does not use the term “liberal arts college”). Let us know if you would like some suggestions for other schools.