AOPA and COPA have put out a good guide for border crossing. You will have more issues going back to the states than coming to Canada. You will have to stop at a point of entry, have them notified head of time, and have a flight plan for crossing the border.
In Canada you don't NEED a flight plan but you need to at least file a flight itinerary with a responsible person. IE, if they don't hear from you, can't get ahold of you, they know how to get the ball rolling for SAR.