Why are some stores like whole foods allowed to stay open on labor day while others can't

I had a couple of sick kids all week so I didn't get a chance to grab some essential groceries all week, now that I have a chance I look online and it seems only the whole foods and rabba are the ones that are open today. Those are the two I usually avoid because of their ridiculous prices, so I was wondering why the cheaper places don't open, and if it has anything to do with Ontario law.