Canadian officials, briefed on the plan on Sunday, promised to aid those affected by the December 2019 closure, part of a wider restructuring plan that will cut production of slow-selling models and slash its North American workforce.
GM said the closure affects 2,973 assembly line jobs in the Ontario city, out of a Canadian workforce of 8,150.
"I spoke with GM (Chief Executive) Mary Barra to express my deep disappointment in the closure," Trudeau tweeted on Monday. "We'll do everything we can to help the families affected by this news get back on their feet."
GM told the provincial government nothing could be done to keep the plant about 37 miles (60 km) east of Toronto open, Ontario Premier Doug Ford said.
"The first thing I said is, 'What can we do? What do we have to do?'" said Ford, referring to a Sunday call with GM Canada's President Travis Hester. "He said the ship has already left the dock."
Ford later added: "We're disappointed in GM. We supported GM years ago when they were in trouble."
The Canadian and Ontario governments joined the United States in supporting GM with billions of dollars in aid after the automaker filed for bankruptcy protection during the 2009 global economic downturn.
The closure dealt a blow to an industry which has struggled to attract new investment in recent years. However, the new trade agreement struck by the United States, Mexico and Canada in September leaves significant room for Canadian plants to grow exports duty-free. USMCA, as the new NAFTA is called, is expected to be formally signed this week.
Canadian Innovation Minister Navdeep Bains said that GM "only made this official announcement to us yesterday."
A former Canadian auto executive said it would be difficult for Canadian government officials to entice GM to keep the plant open.
"The government has done everything they could to keep them afloat. Obviously incentives by themselves don't keep a car plant open," said the executive, speaking on condition of anonymity because of the sensitivity of the matter. "It's all about getting a product mandate," or a commitment to produce a specific vehicle.
Members of Unifor, which represents GM assembly workers, walked out of the Oshawa plant "in protest," ahead of a meeting with GM about the announcement, a union spokeswoman said.
"I've moved my family twice for this company and they do this to me. It's terrible," a tearful worker told CBC TV as he left the plant.
A 2015 study commissioned by the union estimated that shutting the plant would eliminate 4,100 direct jobs and reduce Ontario's gross domestic product by C$1.1 billion.
Shares of Canadian auto part makers and suppliers dropped, with Martinrea International, which supplies to GM's Oshawa plant, falling 6 percent. Magna International and Linamar Corp pared early losses to trade barely changed at mid-afternoon. (Reporting by Allison Martell in Toronto and Allison Lampert in Montreal; Editing by Jeffrey Benkoe and Richard Chang)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)