A cold front will move through southern Ontario Thursday night or early Friday morning. Expect a wet track as activities begin on Friday morning, but most of the rain should be gone by the time the first practice session begins at 9:15 am. The rest of the day will have clouds clearing out, with partly to mostly sunny skies.
Saturday looks great, with pleasant temperatures and mostly sunny skies.
Sunday is still a bit uncertain, as one model is showing some light rain through the day, but other models show dry conditions. There is an upper level trough that will be approaching from the west, which will bring moist air northward into southern Ontario. However, most of the rain should stay south of Lake Ontario. I expect that if there is any rain, there would only be a little sprinkle now and then, and it would have very little impact on the race. I don't expect that it would cause any delays or interruptions, though it may wet the track slightly. If you're going to the track, it might be a good idea to bring some rain gear, just in case.