If there is no TA at the 12th hour (strike deadline) the park brake will be set with aircraft all over Air Canada's world except for those in the air, they will land at their destinations and stay where they are. Flight crews will make their way home and the mess will begin with pax stranded everywhere.
Even if the strike is few days getting the operation back up and running will be a massive logistical problem taking days and weeks to return to normal ops.
Im sure both sides will consider this aspect in the upcoming weeks, hopefully this scenario doesn't happen.