GM also operates manufacturing facilities in St. Catharines, Ont., and Ingersoll, Ont.
"This callous decision by GM to reduce or cease operations in American plants, while opening or increasing production in Mexico and China plants for sales to American consumers, is, in its implementation, profoundly damaging to our American workforce", said Terry Dittes, UAW vice president.
General Motors Co.'s pre-emptive strike to get leaner before the next downturn likely will be followed by Ford Motor Co., which has said it is restructuring and will lay off an unspecified number of white-collar workers.
General Motors had signalled some of its plans previously.
That was followed in 2008 with the closure of the city's truck plant, leading to a almost two-week blockade of GM Canada's head office in Oshawa.
"Representative Holmes said the State Government reached out to GM about what they can do to help them bring a new vehicle to Lordstown, and will continue talks for a new product line to come to Lordstown".
"We started this transformation in 2015", Barra said in a conference call with reporters to announce the moves, "Now we're accelerating and picking up the pace".
"It's going to affect the province, it's going to affect the region".
The closure will reverberate far beyond those municipal borders, as many other Canadian auto part suppliers feed the plant in southern Ontario.
GM said it will take pre-tax charges of $3bn to $3.8bn to pay for the cutbacks, but expects the actions to improve annual free cash flow by $6bn by the end of 2020.
GM did not immediately comment on Trump's remarks, but the company noted it has other facilities in OH including a transmission plant in Toledo and metal center in Parma.
Oshawa NDP MPP Jennifer French said the news of the closure is "gravely concerning".
"GM didn't build #Oshawa".
Ford later added: "We're disappointed in GM".
In a statement released to the media, Unifor, the union that represents workers at the factory, stated that while they don't yet have the full details of the announcement they do know there is no product scheduled to be allocated after December 2019.
Dr. Colin Carrie, the Member of Parliament for Oshawa, called the reports "very concerning".
Production at the plant began on November 7, 1953, and in the 1980s the plant employed roughly 23,000 people. In speaking with GM, we have stressed the importance of supporting their employees through this hard transition. The automaker said the plant is now operating at half capacity and has been hit by the "significant shift in buying patterns away from cars to favour trucks and SUVs".
At the time of the transfer, Dias said Carlisle's appointment to lead Cadillac would raise his profile and influence within GM's headquarters in Detroit, and that "would be a huge benefit for us".
Its operations even became a talking point for US President Donald Trump during tense Canada-US negotiations to revamp a continental trade pact.