I don't recall seeing wild Swans on Lake Simcoe.
I believe these are Tundra Swans - Mom or Dad with 3 fledglings - the other parent is outside the photo. Cob and Pen mate for life and breed in the Arctic tundra. They migrate about 4,000 miles to winter in the US along the Atlantic. The fledglings stay with the parents for about 1 year.
Stay tuned as I'll have more family photos in the coming days.