He shot a closing 70 to finish regulation locked with Marino (70) at 12-under-par 276, one stroke ahead of Mexican Rodolfo Cazaubon (68) and third-round leader Ian Poulter, of England, who carded 72.
Finau played his final eight holes in two-over in windy conditions at Coco Bach to allow Marino to extra holes.
They played the par-five 18th three times in the playoff. Both players birdied the first two times, but Marino could not match Finau's birdie on the third try, when the latter got up-and-down from a greenside bunker, while Marino’s putt from just outside four feet missed to the right.
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"I learnt a lot being in contention (at several tournaments) last year," Finau told PGATour.com. "I learnt you have to take the good with the bad.
"I'm proud of the way I stuck in there and happy I made that last putt when I needed to." Runner-up Marino remained winless in 182 starts on the PGA Tour.
Poulter, winless in four years, closed with 13 consecutive pars and missed an 18-foot birdie putt at the last to narrowly miss out on the playoff.
(Reporting by Tim Wharnsby in Toronto; Editing by Andrew Both)
