What you linked to is a legal opinion by a lawyer who works for a green think tank.  Opinion differs from facts.

Here's a different opinion:

http://ipolitics.ca/2016/07/28/baloney-meter-could-brad-wall-take-ottawa-to-court-over-carbon-tax/

I don't purport to know the outcome should push come to shove. But would predict protracted legal battles and political strife if Justin wants to throw federal weight around.