Had a great answer, but I pushed the wrong button and it went poof. Anyways…
Canadian “Interac” debit cards are realitme, online and immediate; when you approve the transaction and put in your PIN, the money is deducted right then from your account. There’s none of this faffing about with holds and posting later. You choose whether to add a tip and how much before you okay the transaction; then it goes off to your bank and gets approved (or not).
One semi-exception is paying at the pump. You put in your card and enter your PIN; the pump does a debit transaction to pre-approve a certain amount, then unlocks the nozzle. You fill up. The transaction that gets posted is the final amount, though. In any case, the transaction is done when you leave the pump.
Canadian debit cards have always used PINs. This differs sharply from the traditional Visa/MC credit cards, which were signature-based and not realtime. In restaurants, you would present your credit card, the server would take it and run it and bring back a slip, where you would enter the tip amount and sign. Then the charge showed up in your credit card account a few days later.
Most credit-card transactions are handled electronically these days, even if they aren’t real-time; the imprinting machines are pretty rare. Though I saw one in Bancroft a couple of months ago.
A debit card user at a Canadian restaurant would usually have to go to a central cash desk where the terminal was, while the servers would bring the slip and a pen to the credit-card users. This convenience favoured credit users.
Recently, however, both credit cards and debit cards in Canada have been changing to a chip-and-PIN system. A PIN was introduced for use with credit cards.
This change meant that merchants have to replace or upgrade their terminals, and many restaurants have been changing to portable terminals that take both debit and credit cards and operate almost identically for both debit and credit. The server brings the terminal to the table and the whole transaction takes place there, both debit and credit. (Swiss Chalet, notably, was an early adopter of these.) You put in the tip amount at this time.
Canada has never has Visa/MC-branded debit cards. There has been some noise about introducing them here recently, but their biggest disadvantage is that the transactions take time to go through the Visa/MC system rather than being immediate, so it’s possible to put in a whole bunch of charges quickly and overdraw your account in a way that you can’t with Interac.