In the current political environment, I don't think they'll let them walk.
Remember that last year they passed back-to-work legislation aimed at the controllers, more than a week before the legal strike date (the strike would have started during a recess and I guess they couldn't break their vacations).
That's a little different in that these workers weren't allowed to strike before privatization (also that it would have affected all flights using Canadian airspace, including overflights and cargo operations), but postal workers were also legislated back, legislation including a salary increase that was less than management's offer.
I imagine David Collenette will welcome the opportunity to look forceful by keeping the "Canadian air transportation system" (i.e. Air Canada) flying.
andrew