So here's the scenario, I'm a hardcore anarchist going to a demonstration with the intent to cause violence. I'm concealing my face to avoid the legal consequences of my actions and don't care about the other peaceful demonstrators who I probably consider to be sheep anyway. And when I get to the demonstration site and begin to confront the police and am then confronted by demonstrators who want to reveal my face what do I do? My life isn't in danger, there's probably more cops than protestors nearby. If I was an authentic demonstrator I'd simply walk away if it didn't look like I'd be able to start a large scale riot(which was probably the real intent, it would have diverted public attention away from a controversial subject) and protect my anonymity.
What happened is these "demonstrators" by their own violition put themselves into police custody, where if they were authentic would be photographed, fingerprinted and entered into a variety of databases. Something that has much greater consequences in this day than it did even a few years ago. It could limit where they can travel and even wind them up in a security black hole if they were unlucky. Cole is right, these "demonstrators" weren't concealing their identity from the police, they were concealing it from the protestors. They willing gave their identity to the police which makes it likely the cops already knew who they were.
The supreme court has already ruled that Canadians have the right to peacefully demonstrate, if this can be traced back to the PMO there's more than enough grounds for a Charter violation case here. At the very least the opposition would have grounds for a non-confidence vote.