This is called dynamic currency conversion. It’s probably the most frequent mistake people make. ALWAYS decline the rate that is offered.

We don't call 'em "banksters" for nuthin', ya' know.

The actual exchange rate is actually the same at all banks and depends on which international network they use, Visa or Mastercard. It varies a bit between the two. The differences are what the banks charge for their ATMs, what your bank charges for use of a non network ATM, and if your credit card company charges a foreign transaction fee which usually is around 3%. Just get a debit card that rebates ATM charges, offers a large network, (the main ones are plus and cirrus) and doesn’t charge a foreign transaction fee. As long as you’ve got the right card the differences between ATMs isn’t worth worrying about. Of course you always decline dynamic currency conversion

That is such a fine detailed explanation of the 'ATM Process'.
There are so many misconceptions about it.

After going through the steps to withdraw, the ATM displays an exchange rate and asks whether I accept. Somewhere on the screen it notes that this is a 14% markup. That’s right. 14%.

It asks whether I accept the exchange rate. I always say “No’. I let Tangerine do the conversion. On a M$10,000 withdrawal, I have sometimes saved C$100.

I realize that exchange rates change but can someone tell me what the current exchange rate is for the Canadian Dollar at the ATM? Is one bank better than another?

Xe.com is showing 12.74. My experience is that, at Scotiabank on Juarez, you'll get approx. 12.38.....calculated at the xe.com posted rate, minus their currency exchange rate of between 2.5 - 3.0%. At 2.8%, it works out to that 12.38.

Note I don't pay an ATM transaction fee because I am a Scotiabank customer. Using anyone else's ATM, I'd have to pay anywhere from 20 to 60 or 70 pesos extra for each transaction.