January 23, 2007* – Passports, Merchant Mariner Documents (MMDs) or NEXUS Air cards will be required for all air travel, and most commercial sea travel, from within the Western Hemisphere for citizens of the United States, Canada, Mexico, and Bermuda. This is a change from the previously scheduled date of January 1, 2007, to accommodate holiday travel.
*Note that as of June 8, 2007, the US government relaxed passport re-entry requirements due to a backlog of passport applications. Thus, until September 30, 2007, US citizens arriving in Canada by air need only present proof of passport application rather than a passport itself.
June 1, 2009 – The deadline for all Western Hemisphere travel, including land border travel. The specific requirements for the land border crossing will be outlined before this date. Note: June 1, 2009, is the deadline; it's possible - with proper notice - for the date to move up.