Well, even though you restore the whole thing you will still be unable to use it. Reason is the baseband (the software that controls the radio) is locked to AT&T. So undoing and redoing a software will just reinstall this blockage (even if the firmware is from canadian servers).
What you can do is go to Rogers and tell them what happen. Tell them, you need it unlocked from the AT&T lock and locked to Rogers (please do not suggest keeping it unlocked as this might piss them off). I am sure they will do the whole software unlocking thing and relocking to Rogers, but I can't assure that.
Also, you can go to Apple and tell them what happen and see if you can get a refurb iPhone 3G from them with the Canadian lock in exchange for your AT&T one.
Those are the only solutions for you as software unlocks at this time are not possible for the 3G baseband.
Are you suggesting people violate International, National and Federal Laws? You know using a SIM sandwich in an iPhone 3G is highly illegal because there is alot of playing around with network IDs.
Zf_ from the iPhone Dev Team investigated about a SIM sandwich solution and found just that. He concluded its not worth it (due to its highly illegal nature) and works 20% of the time.
Please, next time you suggest such thing, investigate.