Will skies be clear over southern Ontario Sunday night?

Clear skies are forecast.

Also:

Will skies be clear over Earlton, ON during the Aldebaran lunar graze occultation event http://www.lunar-occultations.com/iota/bstar/0710zc692.htm Tuesday morning (time, approx. UTC 08:30)?

Skies may be clearing by occultation time. Forecast models predict a region of moisture at 700 mb level (generally causing mid-level cloudiness) to be moving southward from the Earlton area around 09 UTC but more widespread moisture at the 850 mb level over the area. While humidity generally <70% doesn't mean widespread cloud, upward motion (such as ahead of a warm front) can cause it to be widespread cloudiness, while strongly descending air (such as following a strong cold front) can mean dissipating cloud. In this case, a cold front is forecast to move southward over Earlton overnight Monday night and be near Toronto by sunrise Tuesday but strong subsidence is not forecast following the front. The moisture which is forecast to be over Earlton could dissipate by occultation time, but may remain as a scattered or broken layer of clouds that doesn't dissipate until either dry air moves over it and mixes with the moisture to reduce the relative humidity and cause the clouds to dissipate, or else waits until vertical mixing and convection begins after sunrise to help mix the moisture out and cause dissipating clouds.

In this case for 09  UTC Tuesday, the nearby presence of lots of moisture implies a significant risk of cloudiness (possibly broken overcast or just scattered clouds) until several hours after sunrise. But, it could also be read as clearing skies, and possibly even mostly clear skies, by occultation time.

Below are forecast charts for moisture at 850 and 700 hPa levels from GFS model and latest NAM model.