If you're travelling to the United States, see United States: Crossing the Border. for travel between Canada and the United States, by air, land, or sea.
Documents Needed to Go Between Canada USA by Car USA Today
New laws regarding travel between Canada and the United States recently went into effect in the U.S. and resulted in a change in the documentation required to enter
US Permanent Resident Travelling to Canada — Elliott C. Back
According to the US Department of State, all I need to travel to Canada is my greencard as proof of permanent residency, at least until December 31, 2006. December 31
Canadian US Border Go Northwest! A Travel Guide
Visitor information about crossing the border between the United States and Canada.
Western Hemisphere Travel Initiative
to present a valid passport or other approved secure document when entering the United States from documentation when travelling into Canada by air