In the case of Canada Post, the use of back-to-work legislation to end the labour dispute seems inappropriate. Quite likely, it is a violation of the right to collective bargaining that the members of the union possess.
Losing postal service has not been a catastrophe. It definitely wasn’t too problematic before the management-initiated lockout. As such, the only serious disruption to service that has taken place has been the result of a management decision. Canada Post’s workers don’t deserve to be forced back to work through legislation because of that.