They usually don't verify. By "how strict" do you mean same airline/flight or do you mean totally separate?
I've gone to priority check-in numerous times with my mom, me being either Silver or Gold and her having no status, no problem. Oh and we were on different flights with the same airline.
In terms of security, I did go through I believe it was ATL with somebody that wasn't on the same itinerary. Get to security, "they're with me", and no problems. How they'll deal with it in Canada I'm not sure, but again if the flight is the same, I'm sure they won't start looking at confirmation numbers.