This could be a bit of a pickle for you... where did you get the device?
Was there an AT&T SIM card in it when you got it?
Since AT&T are not bound by Canada's rules for device unlocking (being headquartered in USA), you may wish to engage in a telephone unlocking service available in kiosks in malls or other online-type services.
This may be a buyer beware moment...
Canadian carriers are suppose to unlock for free.
However, since AT&T is a US carrier, it has its own rules for unlocking. Unless you meet the criteria for unlocking, you might be out of luck.
I could but I have encountered this before and I have the "tech" know how to do this so i should be ok i just wanted to see if there would be a easier option then that
If you really believe it's locked to the AT&T network, that might be your only option.
If you got the device from someone you know who WAS the account-holder, they could assist in the completion of the carrier issues.
I'm guessing that's not the case, though.