One of our favorite cruising destinations is Pelee Island, Canada. It is about 25 miles north of Sandusky, Ohio.
US Citizens must clear customs at an official port of entry. Scudder's, Dick's, and Pelee Island West Dock are acceptable. You do this by calling 1-888-CANPASS as soon as you dock your vessel. If you plan to visit several ports on your cruise, you only have to clear at the first marina.
On your return back to the States, you are required to check in with both customs and immigration.