TORONTO (Reuters) - Contract negotiations between Canada's Unifor union and General Motors Co were scheduled to continue around the clock on Sunday ahead of a Monday night strike deadline, the union said, with the two sides still far apart on the key issue of investment.

Unifor GM bargaining committee chair Greg Moffatt said the union and the company were still "miles apart on the key issue - product."

The automaker and the union representing its Canadian manufacturing workers have been divided over union demands that GM commit to new vehicle models at its Oshawa, Ontario, plant.

"I'm feeling much better today than I did yesterday but I'm still not feeling great," Unifor National President Jerry Dias told the Globe and Mail newspaper earlier on Sunday, calling the talks "constructive."

GM did not immediately respond to a request for comment on Sunday evening.

A four-year contract covering the workers of GM, Fiat Chrysler Automobiles and Ford Motor Co in the province of Ontario expires on Monday. The union chose GM as its strike target for contract talks, with any deal setting the pattern for the next round of talks with the other manufacturers.

Contract talks could save 2,500 jobs at GM's Oshawa car assembly or take the plant one step closer to closure. The automaker was already on the verge of shutting one of two assembly lines at its Oshawa plant, with several vehicles either produced in another country or expected to move in 2017.

There are no obvious products that would go into the Oshawa plant, and the automaker said previously it would only make future product decisions after a labor deal.

Canada has been struggling to get new investment from automakers in its once-thriving car industry, losing out to the Southern United States and lower-cost Mexico.

Between 2001 and 2013, some 14,300 jobs were lost in vehicle manufacturing in Canada, according to the Automotive Policy Research Center in Hamilton, Ontario.

Still, the union has said it will not sign without a vehicle commitment, calling it pivotal for the future of Canada's auto industry. Pensions and wages are also on the table.

Without a deal, the union's 3,900 GM members would legally be considered on strike at midnight (0400 GMT) on Tuesday.

(Reporting by Ethan Lou and Allison Martell in Toronto; Editing by Bill Trott and Sandra Maler)