Last month, a Canadian lower court ruled that the Canadian constitution does, in fact, guarantee free trade among the provinces. Here are the basic facts of the case, from the Toronto Globe and Mail:
In 2013, Gérard Comeau was caught in what is likely the lamest sting operation in Canadian police history. Mr. Comeau drove into Quebec, bought 14 cases of beer and three bottles of liquor, and headed home. The Mounties were waiting in ambush. They pulled him over, along with 17 other drivers, and fined him $292.50 under a clause in the New Brunswick Liquor Control Act that obliges New Brunswick residents to buy all their booze, with minor exceptions set out in regulations, from the provincial Liquor Corporation.
And here’s how the court ruled:
Mr. Comeau went to court and challenged the law on the basis of Section 121 of the Constitution: “All articles of the growth, produce or manufacture of any of the provinces shall, from and after the Union, be admitted free into each of the other provinces.”
The judge said Friday that the wording of Section 121 is clear, and that the provincial law violates its intention. The Fathers of Confederation wanted Canada to be one economic union, a mari usque ad mare. That’s why they wrote the clause.
If you are into these sort of things, I highly recommend reading the judge’s decision, which looks deeply into the historical background of the Canadian constitutional provision at issue. Here's an excerpt:
183. That historical context leads to only one conclusion: the Fathers of Confederation wanted to implement free trade as between the provinces of the newly formed Canada. They specifically rejected an American-style of government and adopted continuity with the British system of government at a time when free trade was actively implemented in Britain. Economic development was not only pursued, it was one of the foundational reasons for the pursuit of a union. The repeal of the Reciprocity Treaty with the United States, which was based on free trade, necessitated the search for alternatives. The proposed discussions between Nova Scotia, Prince Edward Island and New Brunswick in September 1864 about possible political and economic union opened up the possibility to replace the American free market with a made in Canada free market for all provinces. The Fathers of Confederation wanted to replace the lost free trade with the United States with free trade as between the proposed provinces of Canada.
I should mention that people who seem to know these things tell me that the decision is likely to be reversed on appeal.