U.S. Department of State

IMPORTANT NEW INFORMATION:   On June 8, 2007, the Departments of State and Homeland Security announced U.S. citizens traveling to Canada, Mexico, Bermuda or countries in the Caribbean region who have applied for, but not yet received passports, can re-enter the United States by air by presentation of a government issued photo identification and Department of State official proof of application for a passport through September 30, 2007. The federal government is making this accommodation for air travel due to longer than expected processing times for passport applications in the face of record-breaking demand.

ENTRY/EXIT REQUIREMENTS:  All persons entering Canada by air are required to present a valid U.S. Passport when entering or re-entering the United States.  Land and sea travelers are also encouraged to have a valid U.S. passport. If they do not have a passport, they should be prepared to provide a government-issued photo ID (e.g. Driver's License) and proof of U.S. citizenship such as a U.S. birth or naturalization certificate.. 

U.S. citizens entering Canada from a third country must have a valid U.S. passport.  A visa is not required for U.S. citizens to visit Canada of up to 180 days.  Anyone seeking to enter Canada for any purpose besides a visit, (e.g. to work, study or immigrate) should contact the Canadian Embassy or nearest consulate prior to travel.  Anyone with a criminal record (including some misdemeanors such as Driving While Impaired (DWI) charges) may be excluded or removed from Canada, and should contact the Canadian Embassy or nearest Canadian consulate well in advance of any planned travel for further processing, which may take some time.

DRIVING IN CANADA:  Driving in Canada is similar to driving in parts of the United States.  Distances and speeds, however, are posted in kilometers per hour, and some signs, particularly in Quebec, may only be in French.  U.S. driver's licenses are valid in Canada.  Proof of auto insurance is required.  U.S. auto insurance is accepted as long as an individual is a visitor in Canada.  U.S. insurance firms will issue a Canadian insurance card, which should be obtained and carried prior to driving into Canada. 

Driving while impaired (DWI) is a serious offense in Canada.  Penalties are heavy, and any prior conviction (no matter how long ago or how minor the infraction) is grounds for exclusion from Canada.  Americans with a DWI record must seek a waiver of exclusion from Canadian consulates in the United States, which requires several weeks to process.  It is illegal to take automobile radar detectors into Quebec, Ontario, Manitoba, the Yukon or the Northwest Territories, regardless of whether they are used or not.  Police there may confiscate radar detectors, operational or not, and impose substantial fines.

For further information - http://travel.state.gov/travel/cis_pa_tw/cis/cis_1082.html.