PLEASE HELP-LANDING IN CANADA

I'm going to land to Canada next week from U.S. by driving. What do I have to prepare before my landing? I have a U.S. green card. I just want to land and come back to U.S. ASAP. So, what do I have to do after I come to Canada? and how many days should be enough to stay in Canada? Will I have problem to come back to U.S.? Thank you very much for your quick responses. I do really appreciate for any advice.