Canadian high school to US colleges

Hey, I was just had questions regarding applying to US colleges as a Canadian international student.

I have noticed how many selective and competitive schools in the US have students with exceptionally high marks. Which is not so common in Ontario (especially my school, it is renowned for being academically rigorous and competitive). I was wondering if any one could fill me in on how canadian high school grades are viewed as in US colleges, because there is definitely a big difference between the curriculum of the two nations.

Thanks!