CPPIB was created for very different reasons. The governance structure is entirely different, such that you have provincial stewards. I'm not sure how you would transplant that model onto Canada Post.
I think if you want to involve all the parties with representation from the unions and the employees and the employer, the proposed target benefit plan, which allows the benefits and contributions to be adjusted up or down as the plan performs is probably a better model than is the CPPIB model.