Article 31 of the Criminal Code permits you to do that if you see a manifestant in a crowd. He's got a mask. He's got a backpack. You suspect...you have reasonable grounds. I cannot believe anybody would think you do not have reasonable grounds. You go to Disney and they open your bags to make sure you're not bringing anything in. I believe you have the tools.
What complicates things is the size of crowds. Suddenly these guys are well hidden. We turn in circles, because I don't see how the new legislation will permit you to do more than what you already can do under the Criminal Code. It's almost an impossibility, unless you just say you don't accept anybody with a mask or a disguise in any crowd. That would be the best way to do it, wouldn't it?