cash back at grocery stores

In 2015 we got cash back from Walmart and Fred Myers in Canada and Alaska.

Yes, from debit card. At least we were able to at some.
Check with your bank to see if they have an affiliate in Canada. Our bank has an affiliate. We use their cash machines to get cash.
When returning to US, we count up all the Canadian money, and pump it in the fuel tank. It is easier then trying to exchange.

Good question. Based on a quick internet search, some US banks suggest that if the card is "chip enabled", that is, has the secure RFID chip in it that requires it to be inserted into a chip card reader, and a PIN number entered to enable transaction processing, then "YES", it should work in Canada, because that's our default process now. One US bank describes it in this recent article. Doesn't say much about cash back at POS locations.

https://www.chase.com/digital/fraud-security/security/faq-debit

When we go the other way, we typically bring some cash with us, only use debit at major US banks for additional cash withdrawals, and use credit cards for the majority of our purchases. Maybe ask your bank if they know? It's probably come up before.

Another link with further info.
https://www.tripsavvy.com/debit-and-credit-card-tips-in-canada-1481710