Canada

This isn't actually all that unusual. Most countries do most of their trade with their neighbouring countries for logistics reasons. To actually implement diversified trade would require the government enact policies preventing Canadian businesses from doing trade with the US, or maybe having export taxes or whatever. A business that can make money selling to the US isn't going to just turn that money down, right? There would be an ongoing cost to maintain those policies, all to avoid a hypothetical future cost of diversifying the economy if that trading partner suddenly went insane.

Now there are things the government could do like developing infrastructure needed to make sure we have the capability to trade with other countries. Like a pipeline from Alberta to the Pacific for example. Perhaps more projects like this should've been done, but these kinds of things aren't cheap and how much money do you spend to protect against future economic problems?

Also they could pursue trade agreements with other trading partners... and that happened too. There's the CPTPP on the Pacific side and CETA with the EU. Unfortunately we're still waiting on EU members ratify CETA, but not much we can do about that.

So yeah, it's a lot of hindsight is 20/20 with this kind of thing. As with most things, the government could have done better, but they did do some things Ok. But having a neighbouring country suddenly batshit is always going to cause trade problems.