this will be slightly tricky, as the surface of lake superior is typically ~320 feet above the surface of lake erie. you might think that you could just build a 350' tall 30 mile wide dam across quebec city but i'm skimming a topo right now and i think it would just try to drain through the hudson. so you would have to connect the adirondacks and the laurentians instead. 90 miles or so. actually now i'm looking at the topo more zoomed out and i think there might be additional problems. who put the mississippi basin so close to the great lakes. there really oughta be some kind of mountain range south of chicago. anyway.
