The NAM is calling for a good old fashioned spring blizzard. Especially for the south/central regions including the Golden Horseshoe. Below is the latest 72hr total snowfall accumulation map (courtesy of Weatherbell). Yes that is almost 24 inches just north of the Hamilton region. Hammer time for southern Ontario is Thursday. Ottawa will see the primary precipitation on Friday.
While I think this may be a little on the extreme side (ya think?), since it's the NAM, I am not going to say it's not going to happen. But what is more likely is that it'll be a sloppy mess of rain, sleet, ice pellets and snow as the GFS model is outputting, ie there is a significant amount of uncertainty wrt precipitation type.
You have fair warning.