Don't see why this is should be a problem.
For what it's worth the INS seem to do an efficient job dealing with travellers from Canada. I don't know if it's true of all Canadian airports, but at YYZ you pass through US immigration before entering the departure lounge, thus missing out the long queues on arrival in the States where you arrive at a domestic gate. I thought this was a pretty good idea and certainley doesn't appear to be an 'anti-Canadian' policy.
I've driven across the border in both directions, about 2 or 3 years ago and been asked to produce a passport (UK citizen) only for the driver. None of the other 4 occupents of the car were checked. The whole US/Canada border situation seemed like quite a loophole at the time - I can understand why they'd want to tighten up, regardless of Sept 11.