To marshal at the Circuit Gilles Villeneuve in Montreal, Quebec you actually pay ACIND for the privilege. The fee is $30 CAD. They provide marshals for most track events though a local club exists that you may be able to join as a volunteer called: A.S.R.Q (association des signaleurs (es) de la region du quebec).
My involvement for the past few years has been limited to F1 at the Grand Prix du Canada. So I joined ACIND and that was that. However, it was my understanding that the $30 membership fee also entitled me to volunteer other events held at the Circuit Gilles Villeneuve at that time which included the NASCAR Nationwide Series and the Grand-Am support race.
Circuit Gilles Villeneuve is a fantastic track which I’ve visited a few times both for racing and while sightseeing Montreal (I’ve driven my rental car on the track in January when it was completely covered in snow and ice).