Montreal had already wrapped up top spot in the East Division entering the game.
Sergio Castillo kicked a 51-yard field goal on the final play of the game, and the Winnipeg Blue Bombers clinched the CFL West Division title with a 28-27 win over the Alouettes on Saturday in Montreal.
The win gives the Blue Bombers their fourth straight division title and home field for the coming West final.
Instead, the Roughriders will host B.C. in the West semifinal, with the winner facing the Bombers in the division final Nov. 9 at Princess Auto Stadium.
Montreal had already wrapped up top spot in the East Division entering the game.
Winnipeg and Montreal met in the 2023 Grey Cup, with the Alouettes winning 28-24.