On Tuesday, Ms. Notley appeared to take credit for the action by Mr. Trudeau’s government.
“We said we would get the pipeline built and we are getting it built,” she said in Edmonton, wearing a button supporting the project and surrounded by members of her caucus. “This deal and this pipeline will unlock investment in our oil sands.”
Mr. Morneau, the federal finance minister, said the government would eventually sell the pipeline, in its expanded form, back to the private sector. The government has suggested that it might even turn a profit.
Polls indicate that Canadians over all are split about the pipeline and the expansion plan.
Mr. Trudeau’s Liberals currently enjoy considerable support in the Vancouver area, but his party has long been unpopular in Alberta — a bastion of conservative politics in Canada, Ms. Notley’s left-of-center government notwithstanding.
Keith D. Brownsey, a professor of political science at Mount Royal University in Calgary, Alberta, said he expected the Liberals might lose seats in British Columbia in next year’s election because of the Trans Mountain deal.
But he said the decision to buy the pipeline will benefit the party on the whole, particularly when combined with its climate remediation steps and its strengthening of environmental oversight of proposed energy projects.
“Mr. Trudeau has probably saved his political career,” Mr. Brownsey said. “You may or may not agree with getting more oil to market. But what good is the federal government if they can’t expand an existing pipeline along an existing right of way? He can now say the federal government has done something.”