In late August, the National Energy Board - an independent regulatory agency that oversees global and inter-provincial oil and gas pipelines - announced it would consider upstream and downstream greenhouse gas emissions in determining whether the Energy East pipeline was in the national interest.
Trudeau's "a lack of interest and leadership" on Energy East could undermine confidence in national unity, said Wall.
With that avenue closed off, Western Canada's oil industry is now counting on Trans Mountain project to help carry crude to the Pacific Coast, where it would be shipped to markets in Asia, as well as TransCanada's long-delayed Keystone XL pipeline, which would move more Alberta oil to refineries along the U.S. Gulf Coast.
TransCanada's decision is also a blow to the ailing economy of New Brunswick province, where the pipeline would have terminated.
"TransCanada will also notify Quebec's Ministère du Developpement durable, de l'Environnement, et Lutte contre les changements climatiques that it is withdrawing the Energy East project from the environmental review process".
In the meantime, Saskatchewan Premier Brad Wall expressed disappointment with Quebec's decision to seek an injunction over the Energy East pipeline.
Natural Resource Minister Jim Carr called the TransCanada's decision to end the Energy East pipeline a business decision.
The 4,500km Energy East pipeline, which would have carried 1.1 million barrels of oil per day, faced stiff opposition from environmental groups and several municipalities in Quebec concerned about possible spills affecting groundwaters and rivers along its path.
The Liberals are defending jobs while protecting the environment, Trudeau insisted during question period, but "the market conditions have changed fundamentally" since the pipeline was proposed, including a steep drop in oil prices, he said. The board said all hearing steps and related deadlines for the TransCanada Corp. project are no longer applicable as the new panel begins its review.
August 19, 2015: TransCanada says concerns raised about Energy East in a report about the potential impact of the project on whales and some fisheries in the Bay of Fundy are unfounded.
But Adam Scott, a senior adviser at the environmental group Oil Change International, had a different interpretation.
The Calgary-based company said previously that it was suspending its efforts to get regulatory approvals for the mega projects.
"We are disappointed with this decision", says Ian Whitcomb, President of Irving Oil.
"This project was so wrong and so unsafe, its hard to believe it was seriously contemplated", Gretchen Fitzgerald, national program director of environmental organization the Sierra Club, said.
"While we ultimately support getting off oil, oil is still necessary today", they said in a statement.
TransCanada's statement didn't blame either the regulatory process or low oil prices for its decision, which will result in a non-cash charge of about $1 billion in its fourth-quarter financial results.
The Nebraska Public Service Commission is reviewing the Keystone XL plans and has until November 23 to decide whether to approve or deny the project.