There's 2 FleetNet Zone 3 towers on the Island there - West Bay, Silver Water. Killarney tower might also get picked up, depending where you are on the island. There's a talkgroup for OPP - 8592, covers Manitoulin. EMS might be the Sault St Marie talkgroups?
I’ve spent lots of time on Manitoulin. Program those three towers mentioned above on and you’ll here all FleetNet on the island.
Killarney will get you some chatter while you’re on the East end of the island.