Will skies be clear over southern Ontario Sunday night?

It looks like skies will be mostly clear during the evening, except for some low-level clouds over southern Ontario during the afternoon that might persist during and after sunset before dissipating, and except for some high cloudiness that will cause mostly cloudy skies in southwestern regions by sunset and will be gradually increasing overnight over the rest of southern Ontario.
Over regions east of southwestern Ontario, the high cloudiness may cause visible high clouds at some times and other times not be visible, until increasing mid to high-level moisture spreads eastward over southern Ontario (illustrated below for the hour after midnight) and causes mostly cloudy skies by morning over most regions.

Will skies be clear over southern Ontario Saturday night?

Clear skies are expected over most regions, resulting from dry air and subsidence ahead of a strong high pressure ridge, except for partly cloudy conditions south and southeast of Lake Huron and Georgian Bay, where lake-effect cloudiness is likely to form.

Will skies be clear over southern Ontario Friday night?

Skies are likely to start clearing before midnight, as moisture moves southward (illustrated below) following passage of a strong cold front. Skies will most likely be mostly clear after midnight, except for lake-effect cloud over many regions south of Georgian Bay and Lake Huron (illustrated below).

Will skies be clear over southern Ontario Saturday night?
Partly clear skies is the best description for skies that will most likely have some cloudiness at low and mid levels. The illustration below shows some moisture forecast at mid levels during the evening, but it should be considered as an example of the situation at most levels, any time of the night, since some moisture will be present to cause some clouds in the sky over any particular region.
So, in summary, partly clear skies are likely with some cloudiness.

Will skies be clear over southern Ontario Thursday night?

Mostly cloudy skies seem likely, except for less cloudiness in regions near and north of GTA, and eastward over eastern Ontario. A region of moisture at lower and mid-levels (illustrated below) is forecast to move eastward over southern Ontario Thursday night ahead of a weak mid-level trough and this moisture is likely to appear as cloudiness. Regions near and east of GTA will likely have less cloudiness during the evening, until the moisture and cloudiness moves eastward over eastern parts of southern Ontario later in the evening.
In summary: partly clear skies near and east of GTA during early evening, mostly cloudy elsewhere over most of southern Ontario.

Will skies be clear over southern Ontario Wednesday night?

It looks like skies will most likely be clear over southern parts of southern Ontario during the first several hours after sunset, and then become mostly cloudy by about mid-evening. Elsewhere, skies are likely to be cloudy by evening. 

Clear skies following Wednesday afternoon’s cold front will be followed by increasing low and mid-level moisture which is forecast to move eastward across southern Ontario during early evening (illustrated below at EST 19:00) and the moisture is likely to cause skies to become mostly cloudy over most or all regions by about mid-evening.

Will skies be clear over southern Ontario Monday night?

Some clear skies are likely over some regions during the early evening, due to the dry air causing the partly clear skies Monday afternoon, until more extensive cloudiness spreads over most regions by late evening. Some mid and high-level clouds will most likely be visible during the early evening, due to moisture at mid and upper levels over many regions (illustrated below for the 500 and 700 hPa levels) as well as some patches of uplift (not illustrated) contributing to form clouds from the moisture. Low-level moisture is likely to be more widespread later in the evening (illustrated below for late evening at the 925 hPa level) and this is the main factor that is likely to cause more widespread low-level clouds later in the evening over most regions of southern Ontario.