We went in June (the second time I’ve been up there). I went to eat at Restaurant at Pearl Morrisette for my fortieth birthday:
Pearl Morrisette is probably impossible to get into at this point, but they are making some of the best Chardonnay I’ve had too. It was markedly better than the previous time I went years ago.
All of the best wineries follow The Bruce Trail close to Jordan. The big ones are Tawse and Cave Spring. Smaller wineries making amazing wine are Cloudsley, Walters Vineyard/Bachelder (they share a production facility), and Megalomaniac. We also visited 13th Street Winery and was impressed with their méthode Champenoise and Cab Franc. Read good things about Leaning Post, but it was too far away. Closer to town, we actually loved the dirt cheap Team Canada Cab Franc from Pillitteri. It was a great pizza wine.
Have fun. Cloudsley, Pearl Morrisette, and Bachelder are making Chardonnay as good as anywhere.