'I just seemed to be so calm all week, I never got too high or too low,' said McMillan, 26, who collected the winner's share of $24,000 (Canadian) for his third career victory.
Scaletta made an early move with a birdie on the opening hole to pull within two strokes of McMillan, who led at 11-under. McMillan chipped in for birdie on the second then immediately gave the shot back with a bogey at the third. But Scaletta bogeyed the fifth and the eighth, while McMillan birdied the eighth to return to 12-under.
Although he birdied the ninth to close the gap to four strokes at the turn, Scaletta couldn't make up any more ground playing even-par golf on the back. McMillan shot a one-over 37 on his inward nine, more than enough to secure the title.
McMillan, winner of the Canadian Amateur Championship in 1996, earned his first Canadian Tour title as an amateur at the 1996 Manitoba Open. He won his second as a pro at the 2000 Vancouver Open.
Craig Matthew was the last Canadian to win on tour. He captured the Ontario Open Heritage Classic last July.
Scaletta, making his Canadian Tour debut after qualifying for this week's event on Monday, closed with a 72 at the Barefoot Resort's Greg Norman course.
'I am pleased with the way I played,' said Scaletta, 26, who was working as a bartender in Richmond, Virginia. 'I have to hand it to Rob. He was solid all day long -- he's a very good player.'
Rookie David Hearn carded a one-over 73 to finish at seven-under 281. His third-place showing marked his best result on the Canadian Tour.
'I hung in there all day, I just didn't give Rob the run I wanted to,' said Hearn, 22. 'But my confidence is definitely increasing, and I am proving I can compete week in and week out. Hopefully I can take it one step further and win soon.'
Sunday also featured a hole-in-one by Michael Henderson, who aced the 194- yard, par-three third hole, and a double-eagle by Australia's Scott Hend. Hend holed his second shot from 267 yards out at the 571-yard, par-five fifth hole. Moments earlier, the Aussie had taken a triple-bogey on the par-four fourth.