Environment Canada issued a heat warning for Toronto on Sunday, saying temperatures with the humidity will feel like close to 40 Celsius at times.
Meteorologists project temperatures will reach 32C on Sunday, feeling like 38 to 40C, while the mercury will hit 31 to 33C on Monday with the humidity making it feel like 39 to 40C.
They say the high temperatures will increase the risk of air pollution or smog.
"The risks are greater for young children, pregnant women, older adults, people with chronic illnesses and people working or exercising outdoors."
Everyone who is able should limit their time spent outside, and outdoor workers should hydrate well and take regular breaks in a cool place.
The City of Toronto says three cooling centres will be open Sunday afternoon at Metro Hall on John Street, Malvern Recreation Centre on Sewells Road and Masaryk-Cowan Community Recreation Centre on Cowan Avenue.
Metro Hall will be open 24-hours during the heat warning.
On Monday, Mimico-Coronation Club on Judson Street will also be open to the public as a cooling centre.