" ... The Sault Sainte Marie International Bridge (visible as a thin white strip) spans 4,5 km and is the only vehicular crossing between Ontario and Michigan. ..."
Ummm, that's incorrect - the Ambassador Bridge (Detroit MI/Windsor, ON) and the Blue Water Bridge (Port Huron, MI/Point Edward, ON) - also the Detroit-Windsor Tunnel - are also vehicular crossings between Michigan and Ontario.