The Climate Prediction Center in College Park, Maryland is forecasting below average temperatures for the Great Lakes region during the period of October 14-18. Although their data and forecasts officially only cover the United States, the outlooks can be interpolated into Canada.
They also state that "Incidentally, some lake-effect precipitation is favoured for the Lower Great Lakes, but it is a bit early in the season for accumulating snowfall."
In their Risk for Hazardous Temperatures, the Climate Prediction Center is also showing a Slight to Moderate risk of much below normal temperatures across much of the Great Lakes, which would also affect Southern Ontario.
They explain in their discussion that "an area of the East has the potential for overnight temperatures to dip into the 30s (ºF), which would be cold enough to support a first frost over many areas with susceptible vegetation."