I do know there will be a Passport required for Canucks to go to the USA as of January 1, 2007.

"Documents for U.S. Citizens--Bring your passport if you've got one. A passport is the easiest and fastest way to enter Canada and return to the U.S. Note: Under the new Western Hemisphere Travel Initiative, as of December 31, 2006, all travelers to and from Canada will be required to have a passport or other accepted document that establishes the bearer's identity and nationality to enter or re-enter the United States. Other documents that the U.S. government anticipates will be acceptable for land and border crossings under this new initiative are SENTRI, NEXUS, and FAST program cards (international frequent traveler programs). This means that you will no longer be able to enter Canada using a driver's license and birth certificate.

For the latest information on passports and entry requirements for U.S. citizens, check the Web page of the U.S. State Department at www.travel.state.gov. Naturalized citizens should carry their naturalization certificates. U.S. citizens don't require visas to enter Canada."