The rain is expected to start later in the day and become more intense in the evening and overnight.
Heavy rain is expected Wednesday in southern Quebec and eastern Ontario, as the remnants of tropical storm Beryl continue their journey north.
Environment Canada issued several rain warnings for Wednesday and Thursday that especially target Montreal and Toronto.
Forty to 80 mm of rain is expected, depending on the area, but localized rainfall amounts could be higher.
Flooding is possible with torrential rains, Environment Canada warned. The low pressure system will be accompanied by moderate winds.
Early Wednesday morning, the system was already over southeastern Ontario. The rain is expected to start later during the day in Quebec and become more intense in the evening and overnight.
According to the United States National Hurricane Center, Beryl is now a post-tropical cyclone. At its peak, in the Caribbean, Beryl reached the strength of a Category 5 hurricane.
The storm reportedly left 11 dead in the Caribbean and seven in the United States, six in Texas and one in Louisiana. The precipitation also caused extensive material damage and deprived millions of people of access to electricity.