One of the ways to enter Canada from the United States is the Ambassador Bridge between Detroit and Windsor, Ontario.
What is unique about this crossing is that it is the only crossing from the U.S. to Canada that heads south. All others crossings are in a northerly direction.
I really like the old-timey feel of this bridge. A new bridge has been begun, but it is currently tied up in court because the bridge is privately owned. I crossed here in January 2010 and January 2011 to curl in Windsor, and the new ramp on the Detroit side has seen no additional progress.