Visitors from the USA:
As of June 1, 2009 you are required to carry a valid US Passport to enter Canada.

Other accepted documents include:
* NEXUS card
* U.S. Passport Card
* New York State Enhanced Driver's Licence (EDL)

For more information, please visit Travel.State.Gov or The Canada Border Services Agency.

Citizens of Other Countries
Citizens of other countries who wish to enter Canada through the United States must also carry a passport and may require a visa, which they should obtain from a Canadian embassy or consulate outside Canada before attempting to enter the country.

For a listing of countries from which you would need a visa to enter Canada click below:
http://www.cic.gc.ca/english/visit/index.asp

For more information about obtaining a visa click below:
http://www.cic.gc.ca/english/visit/index.asp

For a complete listing of embassies, consulates and missions around the world click below:
http://www.cic.gc.ca/english/visit/index.asp