See: http://www.getyouhome.gov
The Western Hemisphere Travel Initiative (WHTI) requires U.S. and Canadian travelers to present a passport or other document that denotes identity and citizenship when entering the U.S. WHTI will go into effect June 1, 2009 for land and sea travel into the U.S. WHTI went into effect for air travelers on January 23, 2007.
Canadian Citizen’s Click here for more info
