How can a retailer ask for a PIN number on an Apple Pay transaction? They don't even know what account the money actually comes from, since Apple Pay only gives them a one-time use number for that single transaction. So how can they verify a PIN number in that context?
My experience using Apple Pay with a checking account's debit card at Whole Foods Market and Trader Joe's is that it only saves having to swipe/insert the physical card. I'm still required to enter the pin. Sometimes it gives me the options of "VISA Debit" or "US Debit" which both work the same way. A few times I've gotten lucky and it gives me the option of "Credit" or "Debit" and when I pick "Credit" it's a toss up -- probably driven by the amount of the transaction -- on if the transaction is complete or if I have to "sign" with the stylus on the POS.
Canadian? I'm betting this is a terminology collision—US debit cards use credit-card protocols to talk to banks, while Canadian debit cards ("ATM cards" or "client cards") use their own protocols for POS transactions, which Apple doesn't even bother supporting.
Instead, to support Canadian debit cards directly, Apple would seem to be using the Canadian banks' web payments infrastructure (Interac EasyWeb)—which is effectively a SAML auth flow using your card number + PIN as credentials.
Before this mechanism was introduced, Apple did first support Canadian "Visa debit" cards, though, so earlier Canadian users of the system—who have their phone pointed at a Visa debit card number they have, instead of their debit client-card number directly—might be confused by the assertion that Canadian debit card use on Apple Pay requires a PIN. It doesn't, for them.
I have the same experience as @TomSawyer, when a retailer supports NFC payments, but doesn't specifically support Apple Pay, it's hit or miss if it will require a PIN # or not for debit card transactions. For Credit Card transactions it doesn't always require a signature, but it does sometimes.
The retailer doesn't know what account, but the bank DEFINITELY does know.