They don't have true debit cards here.
They have "fake" visa and mastercards. I say that because they aren't at all regular charge cards - they are debit cards, but look just like a visa/mastercard. I think it's because visa/mcard pays promotional money to the banks to have their logo, etc.
They are terrible, because the fraud or ability to drain your bank account if your wallet is stolen is much greater!
Anyway, the difference is that when you use your fake visa, they swipe the card like a credit card and you sign a little slip of paper. The funds come directly from your bank account. Most do not have key pads where you punch in your PIN.
However, some now do have the punch pads for PIN - big grocery stores and
walmart, target, etc. But the problem seems to be that it doesn't allow that step where in Canada it asks to withdrawl from cheque/saving or other. This is where the Canadian debit card may not work. Plus if you hand them your card without a visa/mcard logo on it - they haven't a clue what it is. Your debit card may work at those larger stores, but I wouldn't rely on it. We still have our account at a Canadian bank, and my debit card wouldn't work at Walmart.
If you use an ATM, just make sure you withdrawl your maximum amount at the machine as they will charge you a fee anywhere from $2 - $4 US per transaction. Try to not use the machines for small withdrawls.