Will skies be clear over southern Ontario Sunday evening?

It looks like the best answer is partly clear, due to low-level moisture causing low clouds that may occasionally cause partly or mostly cloudy skies, and occasionally clear skies, during the evening. Another layer of extensive moisture higher in the atmosphere is also causing mid-to-high level cloudiness and this will also occasionally cause some cloudiness to appear, increasing the chances of skies being partly cloudy over some regions.

The charts below show the forecast locations for more extensive moisture during the evening.

Will skies be clear over southern Ontario Thursday evening?

It looks like a situation with gradually increasing high cloudiness over southern Ontario during Thursday afternoon and evening. Some regions may see mostly clear skies during some periods during the evening while other regions may be under thicker cloud. The moisture and cloud cover spreading eastward (ahead of a low pressure trough west of the Great Lakes region) will probably cause mostly cloudy skies by about midnight, but a significant result of the warmer air spreading across southern Ontario will be very steady seeing conditions during the evening. The result may be excellent conditions for viewing planets (as well as double stars), at least in the regions where and when the cloudiness is thin enough.  The cloud forecast chart below shows a good estimate of the gradually increasing cloud cover spreading eastward over southern Ontario.

Will skies be clear over southern Ontario Wednesday night?

Clear skies are expected under a strong high pressure ridge, except for some high-level moisture that is forecast to gradually spread eastward over southwestern Ontario overnight ahead of a warm front. The jetstream-level moisture may appear as cirrus cloudiness by morning over some regions. Below, a chart shows the location of the high pressure ridge axis west of southern Ontario (chart from weather.rap.ucar.edu). Northwesterly winds, dry air and subsidence east of the ridge will be contributing to clear skies. The chart of 250 hPa-level moisture shows increasing potential for thin cirrus cloudiness to appear over southwestern regions.

Will skies be clear over southern Ontario Wednesday night?
It looks like mostly clear skies are expected during the evening, especially over southern regions of southern Ontario, while partly cloudy skies are expected further north, closer to a large region of mid-level moisture forecast to be over the Lake Huron region, ahead of a low pressure trough developing west of the Great Lakes region. The chart below shows one forecast model's depiction of mid-level moisture that will likely cause mid-level cloudiness to be visible over some parts of southern Ontario during the evening.

Will skies be clear Monday night during the lunar eclipse anywhere over southern Ontario?
No. (High confidence forecast.)
Low pressure trough and cold front, clouds and precipitation moving eastward across southern Ontario.
The prognosis chart below shows the position of the trough, cold front and precipitation. 

Will skies be clear anywhere over southern Ontario during the lunar eclipse early Tuesday morning?
Not likely. An upper level trough over the central Great Lakes region and surface low pressure trough moving eastward across southern Ontario at the time of the eclipse are forecast by all of the major forecast models to cause overcast skies with precipitation during the eclipse period.
(No supporting charts shown, since there's nothing optimistic to show.)

Will skies be clear over southern Ontario Friday night?
It looks like skies may be partly clear for several hours after sunset, and then mostly cloudy by midnight due to increasing mid-level cloudiness ahead of an upper level trough that is forecast to move across southern Ontario overnight. The charts below show the forecast moisture and vertical uplift at the height of mid-level cloudiness Friday evening.

Will skies be clear over southern Ontario Wednesday evening?

It looks like partly or mostly clear skies are expected during the evening, particularly over southern regions of southern Ontario, followed by increasing cloudiness overnight. Enough mid-level moisture is forecast to cause some mid-level clouds during early evening that will be easily illuminated by the bright waxing moonlight and cause a partly cloudy sky.