Fall colours are at peak in Algonquin, so that's either good or bad. If you want to catch the fall colours at the same time, that would be good. If you hate crowds, then it's bad. Algonquin will likely be a zoo this weekend.
It does sound like some good birds have been found in the Prince Edward County region. The long weekend crowds shouldn't be as bad, since it's a little warmer down there and the colour change is less. We camped at Presquile a few years ago on the long weekend and it was fairly quiet. The rain probably didn't help.