No, Turd, you cannot mountain bike the Bruce Trail. It is meant for hikers. That said, it is possible to stealth camp on the Bruce Trail. I've done that several times. Once I was heading for Niagara, and I got to a town just outside, but it was getting late. I think it was Jordan, Ontario. I biked up the road, found the link to the 'Bruce' and walked my bike a over trees and rocks until I was well away from the road and set up my hammock for the night. Another time I was biking a rail trail where the 'Bruce' crossed. Again I found myself on land that was marked for the trail and was not private land, so it was great for stealthing. That time I ran into a bear, so it wasn't as great.

Often bike trails parallel the Bruce Trail. I suggest you find some good maps.