Good morning Liam,
Certainly a very good question. I cannot speak for the Aussies as I am not an expert, nor profess to be, an expert on Aussie Labour Law. But I do know a thing or two about Canada.
The reason the recent waiver letter does not apply to Canadian based pilots is due to the fact they are in negotiations. CX is not allowed to facilitate any changes whilst these negotiations are going on. It is against the law.
I doubt there will be anything in our new COS to allow for px'ing n the freighter so I have no concerns. That being said, I suspect CX may eventually try to wrap it in a supposed gain in order to get pilots to agree. Let's remember that their rostering and crew management is very amateurish so flexibilities such as freighter px'ing gives them the latitude they need.
You may recall that CX tried to impose SLS the last time on the YVR cabin crew with no success. In Canada, one must follow a certain protocol when trying to facilitate change. You cannot just impose it. Of course, they huffed and puffed, but in the end just walked away.