There are about 80 miles of trails on the Island. They are mainly tight and twisty, with a few faster sections. Some nice scenic stops on bluffs where you can look out over the water. A few years ago me and a buddy stayed in Kinross (south of SSM) and rode to Detour, took the ferry over, rode about 1/2 the Island, had lunch, rode the rest of the Island, then made it back to Kinross by 6-7PM. I think our trip total was maybe 180 that day. So a day trip from SSM to the Island and back isn't out of the question. Or vice versa if you decide to stay on the Island. You can also go from Drummond to Canada via the ice bridge when it's "in season".
They are not in the LES belts so they'll need some system snows for good trails. I've cancelled more than one trip to the Island because of that.
I'm not sure riding just the Island would keep me occupied for three days but as long as there is good snow there are other places to go.
Have fun!