The Senators ended their preseason schedule at 4-3-0 while Montreal dropped to 4-2-1.
Mike Hoffman scored in the first period and Curtis Lazar had an empty-net goal for Ottawa, which also beat Montreal in overtime on home ice Friday night.
Max Pacioretty and Andrei Markov scored for the Canadiens.
Canadiens right winger P.A. Parenteau left in the first period with a lower-body injury and did not return.