Travel from Canada to US

I am currently a F1 student in US and get an offer from Canada. But I will need to travel a lot to US in the future. So I wonder whether it's possible to apply for a US multiple-entry visa so that I can come back anytime I want to.

Also, I heard once I get the Canadian permanent residence(like a Green Card), I can travel as I want(for visits less than 30 days). Is that true? And, do you guys have any ideas how fast I can get the Canadian Green Card?

Thanks a lot in advance!