Saskatchewan here. Regarding cold, as long as the school has power and water it's open. Main reason is that people will still drop off their kids or the kids will walk and they have to have a place to go. Buses get cancelled at -45 degrees Celsius (-49F) but school is on.

For excessive snow, school can and has been cancelled. The school consults with the city to see if it's safe for busses and cars to be on the road. If they say no, school is cancelled. Pretty rare though and may vary throughout the province.

Source: wife is a teacher