The Troll Under The Bridge (Forbes.com) Forbes.com - The main border between the U.S. and Canada, our number one trading partner, stretches for 5,500 miles. The most precious fraction is tucked into the middle of the Great Lakes, where the Detroit River bisects the U.S. and Canadian auto industries. Between Detroit and Windsor, Ont., at the river's narrowest point, lies a ribbon of reinforced concrete roadway, 47 feet wide and less than 2 miles long, laid on suspended steel joists:the Ambassador Bridge. ...