"...plink near Barrie..." The MNR has decided that the only reason to have a firearm in the bush is for hunting. It considers plinking to be the same as hunting. Nearly all of Southern Ontario is owned by somebody, usually people from TO, and most is posted. That requires written permission from said land owner to be there. Any gravel pit will be posted, period.
The OFAH has somehow gotten control of the Simcoe County Forest, not far from you, so you must be a member to shoot there. Other Crown Land is infested with assorted riff-raff like picnickers, hikers, bird watchers, skiers, etc. so you must know exactly who and what is behind any back stop you set up, out to several miles.
Like the others have said, it's far less trouble to join a club. CFB Borden used to let non-CF people into their Rod and Gun club. Lets you hunt(great, big, deer live on the Base. The R&G club feeds 'em in winter.) on the base with 8 hours, I think, of conservation work. No idea if they still do it though.