Sorry, I can't help myself here. Isn't the blanket protection the best protection that you can give? It's kind of like knowing that journalists are going to protect their sources, because why would anyone talk to them otherwise? This is the same thing. Why would anyone talk to a security agent if there were some doubt about whether there was explicit enough protection.
If you go into a seedy bar and someone sidles up to you and says, “Guess what one of my buddies did? And by the way, if I tell you this, do I have explicit protection?” I just don't see this working in practice. Everybody has to know that if you help out a security agency of Canada, you are going to be protected, just like journalists will protect their sources. Then everybody knows where they're at. There's no question about whether this protection is explicit enough, or maybe it isn't, and do they have to worry about that.
I think you're getting into a really unworkable situation.