Thanks for your guesses, so far I came too. I expected someone here might have flown the Canadair or at least been in a cockpit and asked the question.
For instance is the indicator a simple outside sensor reader, or a more sophisticated device coupled to the flaps settings ?
Because seen the aircraft flaps size , Vs must vary a lot with out without them, (and as you can see on the video, they almost always apply some flap seetings during their manoeuvres.)