Martinrea to close Ontario plant in wake of GM cuts, report says Martinrea to close Ontario plant in wake of GM cuts, report says November 28, 2018 dzadmin Comments 0 Comment Martinrea’s factory in nearby Ajax, Ont., supplies GM’s Oshawa plant with parts for the Cadillac XTS and the Chevrolet Impala, according to The Globe and Mail. Neither car will be made beyond 2019.