It's an exit taxes, but as far as I'm aware, it simply taxes you on all assets as if you disposed of them the day you leave.

That doesn't seem particularly unfair. If you can image a scenario where someone buy Apple at $1, and it's now worth $1,000. They just leave Canada, pay no tax, then sell in a low tax jurisdiction.

However, it can be a massive pain in the ass for illiquid assets or assets you don't intend to sell at that point in time. A good example might be a pension. Getting hit with a tens of thousand dollar tax bill for a pension you won't receive for another 2 decades is painful.