Here is what I found,
"Following a consultation period, they will be implemented in three phases:
* As of Dec. 31, 2005: All travellers must show their passport when stopping over in the U.S. during air and sea travel to or from the Caribbean, Bermuda, Central and South America.
* As of Dec. 31, 2006: The rules take effect for all air and sea travel to or from Mexico and Canada.
* As of Dec. 31, 2007: The rule applies to all remaining travel, including land crossings. "
This is at this site