Of course I can't assess what a cost would be, but I would like to point something out. In the current CEPA, the precautionary principle cites cost-efficiency and cost-effectiveness, even in a piece of legislation that was a very significant achievement for environmentalists. The CEPA clause says that “where there are threats of serious or irreversible damage, lack of full scientific certainty is not a reason for postponing cost-effective measures to prevent environmental degradation”. That's a very unusual thing for Parliament to install in legislation. So you don't have to prove your case before you can move to mitigate the damage.
The Canadian Chamber of Commerce is actually quite a strong supporter of that provision, and it's not present in this law. Cost-effectiveness is surely a logical provision in any act, especially if you're giving guidance to judges who are going to issue the order.