Sault Ste. Marie — "the Soo" — sits at the narrows between Lake Superior and Lake Huron, connected to its American twin city by the International Bridge. It is a gateway to Northern Ontario's wilderness, and a surprisingly interesting stop in its own right.
The Agawa Canyon Tour Train is the big draw: a full-day rail excursion through the Canadian Shield landscape of granite, boreal forest, and waterfalls that is particularly spectacular in autumn. The Soo Locks on the American side, and the Canadian Bushplane Heritage Centre — housed in a massive waterfront hangar — are both worth your time.
The city has a strong Italian-Canadian community, which means good restaurants and a decent food scene for a northern town. The waterfront boardwalk along the St. Marys River is a pleasant walk, and on a clear day the views across to Michigan are striking.