Changing credit card for cellular data service
At the risk of seeming prematurely optimistic, that does seem hopeful. I have my Montreal address and even land line phone now, so if the prepaid thing works, I should be able to duplicate your experience.
I don't see why the carrier would care if the card is a prepaid VISA or not. Many people overrun their credit limits on conventional credit cards or run low on funds for a debit card. The debit card that I use for my AT&T 3G cellular data account did not go through because the checking account balance was too low and since it was on Labor Day, the bank wasn't open and I couldn't transfer the funds into that account. I just changed the credit card to another one through the online signup in "Settings", so that presumably would not be a problem if you switch cards.
Also, it might be worth wondering why the carriers would care about the credit/debit card details since they charge each month in full in advance. They really can't lose since if the card ever fails then they can cut off the service. You can't 'run up a bill' because either the account is 'unlimited' or they can also cut you off if you exceed your 250 MB, 2 GB, or 5 GB data usage (depending upon the terms of your plan).
Let's keep the dialogue going until we have a solution or we run out of options. If we find that there is no way to use cellular data in a country in which you are not resident, the

iPad doesn't make as much sense as an

iPhone for the international traveler. At least with a 'locked'

iPhone, you can roam in many countries at a somewhat reasonable rate.
BREAKING NEWS: So, Bell really works? Great, I have a Bell SIM card, too, so when I go to Montreal in three weeks, I'll get a prepaid CDN VISA card and use my Montreal apartment address and I guess that should work. I have a Bell account from my experience two weeks ago, but I never was able to select a data plan. I hope I can revise my Bell account data. Based upon your success, I will probably go back to the

Store in Montreal (which is where I got the Bell SIM) and seek their help.