Environment Canada has issued heat warnings and special weather statements for much of southern Ontario.
The weather agency says temperatures will reach into the low 30s in southwestern and eastern Ontario on Monday and Tuesday.
Environment Canada says there is an elevated risk of heat stroke or heat exhaustion.
It says an overnight low of 20 C will provide little relief from the heat.
The agency says hot and humid air can also bring deteriorating air quality.
The weather agency suggests staying in a cool place, drinking plenty of water and avoiding outdoor activities if possible.