Fall Lake to the Canadian Border and Return is a 28 mile trail located near Ely, MN. The trail is primarily used for canoeing and is accessible from May until September.
I completed this route for one of my classes, for an group with a variety of skill levels, it is a perfect experience. You get the entire BWCA experience from this route without having to go very deep. I went in September which I would highly recommend, the early frosts have already killed off any pesky mosquitoes, tourist season has wound down leaving the lakes open and tranquil, and the weather is beautiful. Watch out for water levels though, low levels can lead to you having to walk your boat through a few parts.