The answer is Costco.

I’ve always heard that people liked working at Costco and around here, around ten years ago anyway, they were known as a good employer.

I got to do a week of first aid for a Costco. Not employed, so just sit in the room and wait. And watch. It did seem like a genuinely happy-ish place, more so after hours when it’s a forklift derby.

I found a version of this on Financial Post that linked the report, I think it's a little bit misleading.

Food Basics being so far down on the list was odd, turns out they were #3 in Ontario, but being branded Super C in Quebec (which was #2 on the National list) makes them two seperate stores. Not really fair. They also didn't include Giant Tiger at all in the report, who might not be a juggernaught in the space but have way more locations and a bigger national presence than T&T, Longos, Farm Boy or Adonis who were included, and it's not as if Basics has a meat counter or bakery either.

https://financialpost.com/pmn/business-wire-news-releases-pmn/costco-ranks-first-in-dunnhumbys-canadian-grocery-retailer-preference-index