today on the Canadian Government travel reports site, they updated passport requirements:
Since January 23, 2007, new entry requirements to the United States affect all Canadian citizens transiting the United States when travelling to and from the Dominican Republic by air. For more information, please see our Current Issues page.
see the whole report at
http://www.voyage.gc.ca/dest/report-en.asp?country=77000 We experienced this when we went back in January, where the customs officials gave some in our party a hard time for travelling without their passport, citing the US legislation. They were eventually let in.
Looks like the times to travel without a passport are over now. Just a heads up if anyone you know is going this route.