Will skies be clear over southern Ontario Sunday night?
Skies are likely to be partly cloudy due to lots of high cloud, due to jetstream-level moisture which is forecast to be over southern Ontario overnight (illustrated below for late evening), and some low and mid-level cloud may also be over some regions during the evening.

Will skies be clear over southern Ontario Friday night?

Lots of cloudiness is likely, due to lots of mid and low-level moisture over southern Ontario overnight (illustrated below for late evening) as well as some high cloud with the jetstream over southern Ontario, but lots of partly clear periods are also likely.

Will skies be clear over southern Ontario Thursday night?
Clearing skies are expected during the evening over most regions as moisture gradually moves eastward from southern Ontario and from regions near western Lake Ontario by about midnight (illustrated below for mid-level moisture during late evening).

Will skies be clear over southern Ontario Wednesday night?
Mostly clear skies are expected except for some clouds that may appear over some regions occasionally due to some low-level moisture which is forecast to be over southern Ontario overnight (illustrated below for late evening).

 Will skies be clear over southern Ontario Friday night?

Cloudy skies are expected over southwestern regions. Further east, partly clear skies are likely over some regions during the evening and will likely allow the moon and brighter stars to be visible before more extensive mid and high-level moisture and cloud moves eastward across all of southern Ontario (illustrated below for late evening).

Will skies be clear over southern Ontario Thursday night?
Mostly clear skies are expected, except for increasing high cloudiness over southwestern regions during the evening and then over other regions later in the night, due to increasing jetstream-level moisture which is forecast to move eastward over southern Ontario overnight (illustrated below for late evening).

Will skies be clear over southern Ontario Wednesday night?

Clear skies are expected, except for some increasing high cloud that may appear over southwestern regions by morning, due to increasing jetstream-level moisture which is forecast to move eastward over the central Great Lakes region overnight (illustrated below for the hour before sunrise).