I meant Burlington, Vermont
The ATT store wouldnt sell me the microsim without an ATT acount

so, you bought you microsim at Wallmart. Ill check to see if there is a walmart nearby
thanks

ok there is a Wallmart about one hour from here.
I checked online on the Walmart web site, and can't find sim or microsim cards. Anyway, you say you bought it in a Wallmart so I'll give it a try tomorrow.
Also I noticed that the person who said you could buy a microsim in the AT&T store is an American, not a Canadian.
I'll post an update. I'll check this thread tomorrow before leaving, in case others have more info to share.
Regards

Yes, I did the research before and it did reveal that Walmart sold it. When I went to the Walmart the attendant there said they had the micro sim card but it was for the iPhone. I was pretty sure it could work so I told her to let me see what it looked like. When I saw it, it was just like I had seen in my research.

I asked her how much it was and she said $24. I told her it should cost $15. She scanned it and it was $15. I knew then it was the right thing. As I said, it has worked. I am using it right now.

Make sure that you have wifi connection to register the credit card and to sign up for the service.

ok, many thanks for the confirmation
perhaps the US ipads come preloaded with the ATT carrier settings, but not the Canadian ones, hence why we need a connection to activate it
I will report back

You can also buy the AT&T sim card at a US Best Buy. That's where I purchased mine when I was in Indiana.

Try an Apple store if there's one near you. In Canada they give you free of charge Bell or Rogers sims. I had ordered mine through Ebay before heading south, when I got to the States it was an easy sign up. Keep in mind that I believe you need to be hooked up on wifi to get the sim set up, if you were not on wifi in the AT&T store this may have been your issue.

Again, no success
Walmart had no stock on microsims, and doesn't sell the iPhone 4 anymore apparently
I'll follow your suggestions above for Best Buy or the Apple store.

best buy did not work
talked to three people there. according to them their ipads and iphones 4 come with the microsim already in the device, they have no microsims on the side

ok, finally! success

went to another ATT store and got a microsim for fifteen dollars

a note to other Canadians who want to try this... the Visa gift card must be "registered" online before you use it.
instructions are on the card

also, I confirm ht you need a wifi connection active to activate the microsim. I was afraid it might require the ipad to be connected to a computer with itunes like Rogers did, but no.

Glad it worked for you, now go ahead and cancel it on the IPad, don't worry it will stay active for the 30 days. This will make sure it does not auto renew next month. If you don't do it before you leave the States you may not be able to cancel easy without AT&T service in Canada.