DETROIT (Reuters) - General Motors Co GM.N will invest 1 billion Canadian dollars in its Canadian operations to expand production of highly profitable full-size pickup trucks to meet growing demand, Chief Executive Mary Barra said on Thursday. The Detroit automaker’s plan, announced after it reached a tentative new labor agreement with Unifor - the union representing hourly workers in Canada - is to bring back production of its Chevrolet Silverado and GMC Sierra trucks to its Oshawa plant, Barra told analysts. The plant was doing final assembly work on pickups that had been partially assembly at GM’s Fort Wayne, Indiana, plant. Strong U.S. demand for pickups, among GM’s most profitable vehicles, helped the company report stronger-than-expected third-quarter earnings. GM also will invest in its St. Catherine’s propulsion plant and the Woodstock parts operation. “We have been operating our full-size pickup plants around the clock to meet exceptionally robust demand for the Chevrolet Silverado and the GMC Sierra in the United States and Canada,” Barra said. “The fact is we simply can’t build enough. And because we expect demand to remain strong, we must increase our capacity.” GM expects construction to begin on the new body shop and flexible assembly module at Oshawa immediately upon ratification of the Unifor deal, she said. The Oshawa plant will come back online in early 2022.