Cars line-up heading into the United States at left and into Canada at right adjacent to Boundary Bay at a border crossing at Blaine, Wash., in July 2009. U.S. Customs and Border Protection agents arrested a British couple who say they accidentally crossed the U.S.-Canada border.

Cars line-up heading into the United States at left and into Canada at right adjacent to Boundary Bay at a border crossing at Blaine, Wash., in July 2009. U.S. Customs and Border Protection agents arrested a British couple who say they accidentally crossed the U.S.-Canada border.