If you haven't already invested in an air conditioner, now is definitely the time to. There's currently a heat warning for Montreal, meaning "humidex values reaching 40 are expected for the next 2 days."
As of Monday morning, the warning was in effect for Châteauguay - La Prairie area, Laval area, Longueuil - Varennes area, and Montreal Island area.
From now until Tuesday, "A hot and humid air mass will affect Southern Quebec."
The government suggests that during heat waves, you drink six to eight glasses of water a day, avoid alcohol, "spend at least 2 hours a day in an air conditioned or cool place," wear light clothing and try to limit your physical activity.
Stay hydrated and stay safe!