I can start.
I wouldn't characterize Visa debit as priority routing, because the consumer does have the choice. What will happen is that on the point-of-sale dialogue.... Today, if you use your debit card, the terminal dialogue will ask you after you've swiped your card—and in this case, it would have to be a chip card, so it would only be applied to a chip transaction—if you want to pay by Visa debit or Interac. You will select Interac by pushing a button on there, just as you do today. The dollar amount of the transaction will come up, and you will confirm that and enter your PIN, etc., and the transaction will be processed. So you have, as a consumer, selected Visa debit.
As Jim has said, MasterCard has taken a different approach and has implemented priority routing. So the bank has issued a card with Interac and Maestro on it, and if it comes to an intersect, a merchant who actually accepts the Maestro MasterCard transaction.... Again, that's important to distinguish: the merchant has to be enabled for Maestro. If the merchant is enabled for Maestro, there is no terminal dialogue in that case, because the bank and the merchant have essentially agreed. The bank has issued a card to a consumer that will be processed by Maestro, and the merchant has agreed to accept Maestro, so in that case it will get priority routed to Maestro versus Interac.