Clearing up a few questions:
A slowdown or work-to-rule is legally equivalent to a strike.
Correction: the bargaining committee has twice negotiated a deal with Air Canada. The union = the membership. The union has not negotiated anything.
The sanction for an illegal strike is a fine of $1,000 per worker per day. If the union does not do everything in its power to persuade the workers to return to work (and the law is worded so as to make that very difficult for the union to do) I believe the fine to the union is up to $100,000.
If Air Canada decides to pursue a legal remedy, the strikers can also be found in contempt of court (assuming Air Canada wins).
Depends on the definition of "private." It's been used against CN workers, against Toronto transit workers, Canada Post obviously, etc. The government does not *generally* interfere in private-sector collective bargaining - the 2009 CAW/Detroit Three is an aberration in that (so far).
Jail time is not a legal sanction for an illegal strike. If that happened, it would be precedent-setting and I think it would take a much more labour-hostile regime and judiciary to bring that about. Technically, a worker who refuses a court order to return to work could be found in contempt, but that option hasn't been pursued since 1978 AFAIK.