What provision? Buying?Like I said earlier: if it simply fails, that is not a challenge. If it fails while ruining the lives of the people it's supposed to save, that's a definitive challenge. If a law ruins lives with little or no benefits that is the whole point of the constitution. Of course, the problem is that it take some evidential foundation to prove the harms and that can take many years.
One last thing about the communication provision: I am not so certain that it is problematic in and of itself. People are making the mistake of looking at separate provisions and thinking this one or that one is problematic. We have to look at it as a whole. Indeed during the Ontario appeal (If I remember correctly), the court ruled that the communication law was not a problem in the context of legal brothels. Likewise, if buying and advertisement was perfectly legal, I think that simply criminalizing the communication near schools could be ruled as reasonable. This would leave enough means to conduct legal business while avoiding exposure of children.
On the other hand, simply removing that provision while leaving buying illegal doesn't change anything at all to the result. To me that provision is a completely moot point when it comes to safety of the worker.
The buying prohibition can render sex work more dangerous if prostitutes can't be more explicit with a menu and a guy feels he's ripped off and goes off the handle. That's just one example.