From recent memory, I think if it's your own bank that you're using the ATM for at a grocery store or wherever, you're charged a lower fee, but if it's a different bank from the card that you're using, you're charged a higher fee. I think that's something that's worth looking into when dealing with Interac.
I know it's a preliminary investigation that you're looking at. In terms of Interac, is it for profit or is it not for profit? How arm's-length is it? Is it at arm's length from the banks? Do they have a stake in Interac?