If you fly into Canada from the US and land you will need to fill out an eAPIS application on line with the US Customs and Boarder Patrol.
Before the flight you will need to call Canadian customs and let them know your plans and timing and get a clearance to land. Likewise on your way back to the US you will need to call US customs to confirm your arrival into the US. You will also need to purchase a $25 dollar sticker from US CBP (good for one calendar year), this will take at least a few weeks to get, but you can us your electronic receipt if you haven’t got it by the time of your trip. You also need a passport and proof of insurance on your plane.
Overall it is a bit of work to get everything figured out, I found the Canadian ATC very professional and helpful (you must file a VFR flight plan if you fly in Canada as well).