Research experience is more important than school ranking, especially when you're from Canada (like me), where even our top schools are not as well known. A school ranked 15th in Canada is pretty low, but rankings in Canada are not "robust" indicators since there are so few programs! I actually don't know what the "top 4 Canadian physics programs" would be -- it seems like UBC, Toronto, and McGill are clearly the top three, but it's pretty hard to pick a 4th school and distinguish it from the others (maybe there is a difference for specific subfields of Physics but not a 4th school in general, in my opinion). However, while in Canada, I think there is a big difference between the top tier (above schools) and everyone else, on the international stage, I think this difference is much blurrier. Our programs are just less known internationally. The Americans I've met might have heard of the big 3 names, but they don't know much about the quality of each program.
I know current and former Canadian grad students at top US schools that came from all sorts of Canadian undergrad programs. It might help a tiny amount if you come from a school that the admissions committee have heard of (maybe collaborated with, had past applicants etc.). So, being from one of the 3 above named schools might help just because those are the 3 bigger schools so it's more likely that the school have seen applicants from your alma mater.
I think that physics education across Canada is pretty similar. However, you might not have as much chances to have really interesting research experiences during your summers at a smaller school (with less resources). I would strongly suggest that you apply for an NSERC USRA at one of the big schools with a strong Physics program. You might have an extra advantage when applying to a USRA at your current school because of any current contacts. Maybe you can even talk to some profs right now about working with them next summer! It could be a good idea to do this before you leave (or at least let them know your intentions so they remember you next year). USRAs are usually due in early Jan/Feb and make sure you know the application process, which could differ for each school.