Actually, my kids have seen several on Beauoliel Island, ( Honey Harbour /Midland area) at the YMCA camp they go to, and the snakes were not captive.
Wow, does that bring back memories. I spent three summers at Camp Queen E in the mid 70s. That was a fun camp, but a rough, tough location- a scattering of plywood cabins on one big rock. I don't know if they still do it today, but back then, the MNR rangers would snag a few of the braver or less imaginative campers to help survey rattlers. It was kinda cool.