A rainfall warning was issued by Environment and Climate Change Canada at 12:30 p.m. today (Tuesday):

Rain, at times heavy, is expected, beginning tonight and into early Wednesday afternoon. Total rainfall amounts of 40 to 60 millimetres are forecast, with locally higher amounts possible.
Rain will become widespread from west to east tonight. The rain will end or taper to scattered showers through Wednesday morning, but may linger into early Wednesday afternoon for locations near to the Ontario-Quebec border.