An interesting explanation of what lead to this was posted by an user on Reddit. (Disclaimer: I'm not from Canada, so I can't confirm/deny what that user said, but there's plenty of upvotes and comments from other canadians lending some credibility to his explanation.)
"This is actually way more complicated than the one paragraph article makes it seem. To fully understand this, you have to know a little bit about Canadian politics. So now I'm going to talk a little bit about Canadian politics.
By some measures, Canada is the most decentralized country in the world, barring absolute anarchies in Africa and all that shit. Power is divided between the Federal Government and the Provincial Governments in an entirely non-hierarchical manner; provinces and the Federal Government each have their own distinct spheres of influence, and the Federal government cannot tell a Provincial Government what to do within the provincial sphere any more than a province could give the Federal Government orders within the federal sphere of influence.
Without getting into huge amounts of details about how power is divided, it's sufficient to say that much, if not all of the powers that would be required to enforce the Kyoto protocol are within the Provincial sphere of influence, however the Kyoto Protocol was signed by the Federal Government essentially unilaterally. So then the Federal Government has to try to bring the provinces on board with Kyoto, to avoid shirking international responsibilities, but it has no power to force the issue. So then, surprise surprise, some of the provinces dont feel like shooting their oil economies in the foot to play ball with a treaty that they never agreed to. Particularly Alberta, which is basically Canada's Texas, decided that the Federal Government had nothing big and scary enough up their sleeve to threaten them into compliance, so they decided they were not going to enforce the Kyoto Protocol internally at all, and the Federal Government could do absolutely nothing about it.
So now it's in a position where it has to either severely cut carbon for every other province that's willing to play along or pay internationally for Alberta's decision to not give a shit. Yes that's right, the Federal government would have to pay for Alberta not meeting the pollution requirements. Not fair? Well then the Federal Government should have made sure people were on board with this before signing instead of bringing home an unpopular treaty it had no power to enforce. OR the Federal Government can drop out of the Kyoto Protocol, as it has done, learn from the mistake and make sure to get the approval of Provincial governments before signing the next environmental treaty that will undoubtedly come up.
TL;DR: Canadian politics is hella complicated, and while no one likes pollution, Peter Kent is 100% right in the article: Signing Kyoto, especially in the way Canada signed it without enough internal support, was a mistake."