To be honest, I am a bit surprised with this decision, since it seemed like the legislative intent around the Constitution Act, 1867 was quite clear. Basically, the question that came up was whether provinces could internally regulate trade, and more specifically whether the Gold Seal Supreme Court case from 1921 had got it wrong by allowing for internal trade barriers when the legislative intent seemed quite clear to not allow for restrictions between the provinces (similar to the absolute free trade between states in the US). Here is a pro-business site with a number of supporting documents, including this persuasive paper. On the face of it, it is hard to understand how Section 121 "All Articles of the Growth, Produce, or Manufacture of any one of the Provinces shall, from and after the Union, be admitted free into each of the other Provinces." doesn't explicitly mean Canada should be a free trade zone, much like the US.* However, the decision at the time was incredibly narrow and said that it applied to tariffs only and that Provinces still could limit the quantity of goods crossing their borders, i.e. enacting internal trade barriers. This has been the law of the land since 1921, even though many feel it was wrongly decided.
Anyway, there was a case about Gerard Comeau who "smuggled" too much beer back from Quebec into New Brunswick, and the lower courts found in his favour, until it finally reached the Supreme Court, where the justices unanimously found in favour of the status quo. Here is a recent article about the decision. I find this incredibly disheartening for several reasons. Number one was that they basically admitted that they upheld the previous ruling simply because it would be too disruptive to too many existing laws and regulations. And it is certainly odd to be so respectful of previous rulings when they are wrong. (Note that when it comes to their own turf, the Supremes have no problem in throwing everything into disarray by setting strict limits on the time to trial, which will inevitably lead to thousands of criminal cases to be thrown out for instance; then doubling down when shown this was causing havoc.) Nonetheless, in the States, if something is found not Constitutional, it will be tossed regardless of the scaffolding that has grown up around it. More to the point, I find this weird balancing that always goes on in Canada, inventing stuff out of whole cloth that doesn't exist in the text (such as a particularly Canadian version of federalism) is unfortunate. I certainly don't like how the Charter Rights are all balanced against each other, rather than there being near absolute freedom of speech (as one finds in the States). I was particularly dismayed to learn about the Notwithstanding clause, which literally allows the government of the day to ignore the Charter Rights (and legal rulings against the government). It basically means that Canadians' rights are always subject to legislative whim and political compromise.
It's this endless fudging at the heart of the political (and legal) system that does make it very difficult for me to wholeheartedly embrace Canada, since I don't think core rights should ever be negotiable. I also think that when a document clearly says one thing (as Section 121 does) then it is really quite pathetic to try to interpret it a different way. I guess we only have to wait another 100 years before the Supreme Court gets it right (and perhaps for the Constitution/Charter to be rewritten to remove the Notwithstanding clause). Not holding my breath obviously. It is a good thing, I guess, that I don't like beer or smokes and so don't have any interest in trying to smuggle them over the Quebec border.
* Not that there aren't some issues with unfettered (or nearly unfettered) free trade, as it generally undermines environmental protection in favour of corporate interests, as discussed in passing here. That said, trade barriers often outlive their initial purpose and are simply maintained to benefit a small number of insiders and thus serve as a drag on overall consumer benefit and societal productivity.