Look at the demand and supply graphs for the 6 day period: https://www.ieso.ca/power-data
The lowest demand is about 12K MW, that is the base load, the load never goes below that. Nuclear and hydro cover that 12K MW constantly, and even hydro is throttles up and down to cover the some of the load that varies throughout the day.
https://en.wikipedia.org/wiki/Base_load
Power plants that do not change their power output quickly, such as some large coal or nuclear plants, are generally called baseload power plants.
Totally predicable for the past 60 years, news?