tells about using Windows Mobile and a Samsung CDMA/GSM phone internationally, but that's not BB by a long shot.
Some parts of the site say Canada/Mexico/PR
coverage is available for voice and SMS, but the coverage map shows no service at all for Ontario/Quebec. Didn't look south of the border.
So, I'd just switch the travellers to Cingular or T-Mobile and put them on an international data plan so you don't have to pay for data roaming. Tack on the discounted international voice and you're all set, no switching devices or phone numbers when folks leave the country, whether it's a short or long haul trip.