USA. Detroit, Michigan. Since the September 11th attacks on the United States, Canada and the United States have accelerated those efforts to protect the security. The two governments continue to expand threat information sharing, upgrade their crisis response abilities and ensure that the Canada-U.S. border remains secure with an efficient flow of trade. The Ambassador Bridge and the Windsor-Detroit Tunnel is a critical link in Canada-U.S. trade, and were used by over 13.4 million cars and 1.8 million commercial vehicles in 2003-2004. 2004.