Regardless of which side of the debate you are on, I think this op-ed by Canadian political science prof Adam Harmes states the issues quite well:
As premiers gather for their annual conference in Winnipeg this week, the issue of reducing interprovincial trade barriers will no doubt be a topic of discussion.
However, for one conservative think-tank, interprovincial trade is an issue best left to the federal government.
In fact, rather than waiting for the premiers to reduce trade barriers on their own, a recent report by the Macdonald-Laurier Institute argues that Ottawa should impose a solution by creating an “economic charter of rights.” While Canadians should say Yes to promoting interprovincial trade, they should voice a resounding No to an economic charter.
...
Proponents of an economic charter argue that it would not affect ... legitimate and necessary regulations. Instead, it would only target the purely protectionist and “silly” regulatory differences between provinces that create red tape for business and provide no real benefits for Canadians. An oft-cited example is the way that different provinces mandate different sizes for the small cream containers we get with our coffee.
While such regulations should clearly be removed, history shows us that there’s no real way to legally distinguish the silly and protectionist regulations from those that genuinely protect Canadians. The closest thing we have to a precedent for an economic charter is Chapter 11 of the North American Free Trade Agreement, which was designed to prevent governments from the outright expropriation of businesses, without compensation, as was done by Fidel Castro in Cuba and Hugo Chavez in Venezuela.
However, clever lawyers were able expand the application of Chapter 11 and use it to force governments to abandon legitimate environmental regulations. Because Canada still has many clever lawyers, there is every reason to believe that the application of an economic charter would be similarly expanded and create similar problems.
He is focused on the Canadian internal trade context, but the same issues apply more generally to international agreements.
Is he correct to say there is no way to distinguish the "silly and protectionist" from "those that genuinely protect Canadians"? I don't think he is, but it is these distinctions that define the boundaries of international economic law, and there's a good deal of disagreement on where those boundaries should be.
