South Koreans Whee Kim and Byeong Hun An, who were tied for the lead with Johnson and Kevin Tway entering the final round, finished tied for second place after both recorded 69s on Sunday.
"I've been playing well the past few months, it was just a weird day, so I hope it's windy tomorrow because I know I can make my way back up the leaderboard". So to get it done here, knowing there were four of us tied for the lead, I knew I was going to have to go out and play a good round of golf if I wanted to win. "It was just bad scoring".
Johnson then birdied his final hole of the day, hitting the par-five 18th in two and needing just two putts to secure his win.
Johnson is also sponsored by RBC, the tournament's main sponsor, so pretty much everyone has to be happy with this result, in what could be last time the event is held at the 7,253-yard, par-72 course designed by Jack Nicklaus.
Johnson said watching 14-time major victor Woods dominate the sport inspired him to create his own legacy.
The American's charge stalled as he struggled with his putter and he had to settle for five consecutive pars before rolling in a 12-footer at the par-four eighth for his third birdie of the day.
Johnson has a strong connection to Canada because of his engagement to Paulina Gretzky, daughter of hockey icon Wayne Gretzky and mother of his two sons.
"Yeah, I mean it's never going to be back here", Johnson stated (confirmed!) "So it was big for me to get the win here".
"It definitely means a lot; I have a lot of ties to Canada with Paulina and her dad and thanks to Wayne I get a lot of fans out here", Johnson said.
"I like the golf course, my game is in really good form, I have a lot of confidence in it but I'm going to have to go out and play really well tomorrow".
Johnson's third victory of 2018 was, like his eight-shot win in Hawaii in January and six-shot win in Tennessee in June, a walk in the park.
When play resumed following a almost two-hour delay, the gap tightened as Johnson recorded a par and An and Kim picked up birdies to cut American's lead to two. "So that definitely boosted my confidence", he said.
He made the most of moving day, sizzling to a 6-under 66 during Saturday's action and mixed six birdies, two bogeys and a double bogey to close Sunday with a 70. He shot 63 on Friday, but had a 73 in the third round. "That was wild", Bradley said.
"Yeah my good shots didn't turn out well but I didn't play good either", Baddeley told AAP after his round.
Nick Taylor was the top Canadian, shooting a 67 to reach a nine-under 135 total.
Tway had a 76 to drop into a tie for 17th at 13 under.
Coming off his first missed cut of the year last week at the British Open, Johnson rebounded in some style to clinch his 19th career title with a winning tally of 23-under 265.