In essence, the Supreme Court upheld the Federal Court of Appeal's decision, in February 2020, which said the following:
Indigenous people have a right to be consulted and accommodated about major projects in their territory, but they do not have a veto. Once there has been a deep respectful process of consultation and accommodation, the federal Cabinet has the right to balance indigenous claims with overall societal interest as they see it.
The federal government has adequately performed that process for TMX, in accordance with the judicial guidance given in 2018. When the Federal Court of Appeal turned down the TMX approval in 2018, and sent it back to the federal government, they identified specific flaws that they said could be remedied by a "brief", "efficient" and "focussed" further consultation. The government did what the court had directed it to do, and, as a result, the approval was amended with significant additional conditions.
Consultation and accommodation are a difficult balancing act, and the federal Cabinet's evaluation of the process deserves deference. The process does not have to be perfect.
The opponents were, in essence, seeking a veto, a right to prevent the pipeline from being built without their consent. Under Canadian law, they do not have that right. Nor can they insist on more years for further study or consultation. The Cabinet can take into account that, of the 129 indigenous communities consulted, 120 support the project or do not object, and 45 signed benefit agreements.
To the best of my knowledge, that means that the opponents no longer have a legal right to prevent the construction of the pipeline. However, they can still make this pipeline slow and difficult to build, and to further damage its economic rationale. The detailed alignment is still to be determined and some environmental studies are still underway. There could be a worldwide campaign to dissuade purchasers from booking space on the pipeline, and from buying oil transported by this pipeline. We may still see a campaign of civil disobedience, people laying down in front of bulldozers and in front of trains across the country.
Opponents can also continue to attempt to persuade the government, and the public, that it is a bad decision to build this pipeline, for economic, climate, environmental and other reasons. Just because the project has been approved does not necessarily mean it has to be built. There has also been considerable discussion about whether the federal government will turn the pipeline over to a First Nations consortium to be built and operated, and if so, how much this would address environmental and indigenous rights concerns.