It found that if General Motors follows through with their plans to close the Oshawa plant in 2020, it will result in the immediate loss of 4,400 jobs at the facility and manufactures which serve it.
"Unfortunately, all Unifor's proposals would involve substantial incremental costs and a further deterioration of GM's competitive position", GM said, adding that "it can not pursue them" because of the weakening market in North America.
"We're going to continue to have discussions with them about solutions", Jerry Dias, national president of Unifor, the union that represents workers at the plant, said after meeting with GM officials at the No. 1 USA automaker's Detroit headquarters.
After meeting with GM officials on Tuesday, Dias revealed in a news conference that the company rejected union proposals to keep the plant open.
"We're looking at tens of thousands of jobs and a direct hit to the GDP", said Unifor president Jerry Dias in a statement.
The General Motors carmaker has had a major presence in the Oshawa area for some 100 years.
GM stunned the North American auto industry in late November when it announced a major restructuring plan that will see up to 14,000 workers in North America lose their jobs, almost 3,000 of which are in the Oshawa Assembly Plant.
An angry Dias spoke to media in Windsor after Tuesday's meeting.
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Auto manufacturing has since declined in the city and will eventually go to zero, the central banker said.
Since GM's announcement, Unifor has launched an extensive public relations campaign, demanding GM save the Oshawa plant.
"Though there was an understanding of the importance of the (Canadian) market and the incredible contribution of our members in Oshawa, they weren't reaching for the solution which is at hand".
David Paterson, vice-president of corporate affairs at GM Canada, told The Canadian Press the union should instead work with the company on timing the transition for affected workers.
"We understand our union's frustration but need to now work together to deliver supports, transition and training for our employees for new opportunities over the coming year", spokeswoman Jennifer Wright wrote in an e-mail.
The union has said the decision is contrary to commitments made by GM in contract negotiations with Unifor in 2016. A large rally is planned in Windsor on Friday.
While the study does concede that there could be a slight uptick in employment across Canada at first as laid off workers move to other parts of the country it estimates that 10,000 jobs will eventually be lost outside Ontario due to a weaker economy.