Here is the thing. In an ideal world, we would have moved over to a plant based system for plastics and gotten rid of the need for Oil and Gas altogether. But sadly, this is not an ideal world. The world has too much supply for Oil, so even if Canada was to stop 100% of its production tomorrow, the world would continue on as it always has and will just move to getting oil from the middle east and other areas.
When it comes to these pipelines, if Trudeau tells Alberta to go fuck itself, Alberta will elect a nutjob to the Conservatives and the Country will elect the fucker because the Conservatives are a major party and the one which takes charge when people are tired of the Liberals. At that point, the idiots will put in place anti-climate policies and we are back where we started, except with a Harper 2.0.
On the other hand, if Trudeau approves some of these pipelines, he gets Alberta on its side and they don't feel as strongly about electing a nutjob to the Conservative Party. On top of this, Alberta will be able to play along with the Liberals Climate Strategy because they had their only demand met.
At the same time, the Kinder Morgan Pipeline is twining an existing pipeline, which is less obtrusive and less dangerous than the Northern Gateway which was cancelled which was going to go through Aboriginal Land just to go through Aboriginal Land and through a protected rainforest because fuck you.
Without the pipelines, the oil still gets produced, and Alberta simply forces it over Rail and Truck which is more likely to cause environmental harm than a tightly regulated and monitored pipeline. So, it sucks, but after looking at all of the statistics... all of the causes and effects of what each individual policy means, and approving these is really the only option.