For all the United States citizens traveling abroad to Canada.....You need to know the facts...
Western Hemisphere Travel Initiative
http://www.getyouhome.gov/html/eng_map.html
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. It is a result of the Intelligence Reform and Terrorism Prevention Act of 2004 (IRTPA).
The goal of WHTI is to facilitate entry for U.S. citizens and legitimate foreign visitors, while strengthening U.S. border security. Standard documents will enable the Department of Homeland Security to quickly and reliably identify a traveler.
WHTI went into effect June 1, 2009 for land and sea travel into the U.S. WHTI document requirements for air travel went into effect in 2007.
Western Hemisphere Travel Initiative (WHTI) and Air Travel for U.S. Citizens
When traveling by air between the U.S. and Canada, Mexico, the Caribbean or Bermuda, you are required to present a U.S. passport, except as noted below. This applies to everyone including newborns, infants and children.
The only exceptions to this requirement are for:
U.S. citizens on active duty with the U.S. Armed Forces, traveling with military ID and travel orders
U.S. citizen merchant mariners traveling in conjunction with maritime business, with U.S. issued Merchant Mariner Document
Travelers with a NEXUS card used at a NEXUS kiosk at Canadian Preclearance airports
U.S. Lawful Permanent Residents with a Permanent Resident Card or other evidence of permanent residence status and required documentation; refugees and asylees with a Refugee Travel Document
Go here:
http://www.getyouhome.gov/html/lang_eng/eng_at.html
Western Hemisphere Travel Initiative (WHTI) and land and sea travel for U.S. Citizens
Starting June 1, 2009, U.S. citizens returning home from Canada, Mexico, the Caribbean or Bermuda, by land or sea, are required to present one of the travel documents listed below. Go Here:
http://www.getyouhome.gov/html/lang_eng/index.html
Enhanced Drivers License : The following states are issuing this type of WHTI-compliant document: Michigan, New York, Vermont and Washington