Do you mean normally it's 21-24 C and it's hotter right now, or that when it's hot it's 21-24 C? 21-24 is within US regulatory safety recommendations, although I don't know Canada's. We threw a fit when the our store started hitting 30 C even when outside was 2-3 C cooler, and they pretty much don't give a shit unless it's 27 C minimum.

That being said, you can refuse to work. Shutting down a store via non-work with clear demands is a valid way to get some change. It might be getting fired, it might be getting the temps fixed. Call in work related injuries, which include getting dizzy or nauseous at work from the heat. You'll call whoever handles workplace injuries for your area, usually can find that info on the hub.

Also, the bit about temperature control being corporate is a lie. Google the thermostat you can find, it'll have instructions for turning down the temp. Usually it's just a temporary change but you can always adjust it a wee.

Goggles?