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Alberta Premier Danielle Smith pushed back on opposition to a pipeline heading East at the Chamber of Commerce of Metropolitan Montreal on Monday.Christinne Muschi/The Canadian Press

British Columbia Premier David Eby is escalating his attacks on Alberta’s proposal for a new oil pipeline to the West Coast, describing the project touted by Alberta Premier Danielle Smith as fictional, non-existent and fantasy.

Mr. Eby released a video on Monday on social media in which he warned that Alberta’s plan to front a pipeline application to Prime Minister Mark Carney’s new Major Projects Office will jeopardize billions of dollars in private-sector investments in B.C.

“The non-existent Alberta pipeline project would put tens of billions of dollars in real B.C. projects and jobs at risk. On top of that, it threatens one of the world’s most precious and intact ecosystems, our beautiful B.C. coast and Great Bear Rainforest,” Mr. Eby said.

Meanwhile, Ms. Smith was in Quebec on Monday, pushing back on opposition to a pipeline heading East.

Last week, Bloc Québécois Leader Yves-François Blanchet said he would denounce any new pipeline from Alberta for “destroying the environment of the whole planet.”

In a visit to the Montreal Chamber of Commerce on Monday, Ms. Smith fired back at the sovereigntist politician.

“It’s no surprise: He wants to destroy the country. I want to build the country,” she said. “That’s why I’m here to talk to the Montreal business community to find ways Quebec and Alberta can be stronger together. … He’s a separatist, so it doesn’t surprise me he wants to destroy the country.”

The Alberta Premier added that she was not currently working on an oil pipeline from her province to the East Coast, a controversial idea last scuttled with the cancelling of the Energy East pipeline in 2017.

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Instead, she said, she was focusing Alberta’s eastern ambitions on Northern Ontario, after an agreement to build pipelines with Ontario Premier Doug Ford.

“I’ve been trying to figure out if we could get to Thunder Bay and then use the Great Lakes maximum tankers to get to a port in Quebec where they could then be loaded for overseas,” said Ms. Smith. “That might be an interim step. I’m just trying to see what the capacity of the Seaway might be.”

It is ultimately the federal government’s responsibility to build pipelines across provincial lines, she argued, hours before meeting with Mr. Carney in Ottawa.

“It is the Prime Minister’s job to show some courage,” she said.

The B.C. Premier has dismissed Alberta’s pipeline ambitions in the past, mostly because it does not have a private-sector proponent. However he largely tried to avoid a direct confrontation, leaving it to First Nations on the coast to fight the application.

Mr. Eby said last week his primary concern is that Canada maintains the current moratorium on North Coast oil tanker traffic. Alberta wants the ban lifted to allow a new pipeline to reach Kitimat or Prince Rupert, but the B.C. Premier says that would undermine First Nations’ support for projects that he wants developed.

This summer, tankers laden with liquefied natural gas began shipping out of Kitimat, B.C. There will be about 170 vessels a year transporting LNG to Asian markets. Meanwhile, the port of Prince Rupert is undergoing a major expansion. The federal tanker ban has been key to securing First Nations’ support for those projects, Mr. Eby said.

Alberta’s pipeline proposal did receive support in the B.C. Legislature on Monday from opposition leader John Rustad, who called on the Eby government to stop creating obstacles for economic growth. “This government seems to think it can run on ideology and unicorn farts,” said the BC Conservative Leader.