Owusa-Ansah picked off starter Jonathan Crompton for a 39-yard TD return at 3:59 of the second and Smith grabbed a Dan LeFevour pass for a 28-yard score at 9:25 for the Argonauts (1-1), who had three picks in the game.
Diontae Spencer had a TD reception and Swayze Waters added 25- and 42-yard field goals. The defence also forced a safety.
Jonathan Bryant scored a TD on the first possession of the game for Montreal (1-1) as he swept around the left side for a one-yard score. The Argos took over for a 22-7 halftime lead.
Trevor Harris, starting for the injured Ricky Ray, played the first half for Toronto, completing 10-of-12 passes for 98 yards.
Gale took over to start the second half and on his first series hit Spencer with a seven-yard TD pass, topped by a two-point convert catch by Lyle McCombs 4:03 into the third quarter. Former Alouette Adrian MacPherson took over in the fourth quarter.
Crompton went 5 for 10 for 71 yards and was intercepted twice while LeFevour went 7 for 14 for 60 yards and had one picked.
Brandon Bridge started the fourth quarter, when Montreal got a 31-yard field goal from Boris Bede. Rakeem Cato played the final three minutes.
Heavy rain started late in the first half and much of the already thin crowd at Percival Molson Stadium, announced as 16,325, left at the intermission.
Montreal opens the regular season at home next Thursday against Ottawa, while the Argos start at home against Edmonton on June 27.
Argos linebacker Akeem Whonder was carted off with an injury on the opening kickoff. In the third quarter, Alexander Robinson was helped off after a low hit from Cliff Coleman.