'This has been a long time coming,' said Hearn. 'To win here in Calgary couldn't be better.'
McKenzie shot a 69 in the final round to take second place at 14-under-par 274. Mathew Goggin was next at 13-under-par 275 while Nick Watney took fourth place at 11-under-par 277.
Hearn, who captured this year's Times Colonist Open on the Canadian Tour, carried a three-shot lead into the final round at Redwood Meadows and managed a pair of birdies on the front side to reach 16 under around the turn.
At the par-4 12th, Hearn left his approach well short of the green and was unable to get up and down to save par. After the bogey, Hearn readied himself for a roller coaster ride over the closing holes.
Hearn birdied the 15th but gave that shot back with a bogey at the very next hole. The 25-year-old recovered with a birdie at the 17th, but found trouble again with a bogey at the last. Despite the late dropped shot, Hearn was able to walk off with a breakthrough win.
'It'll change some of my plans for the rest of the year,' said Hearn, who can now focus his sights on earning status on the PGA Tour for next year. 'I'll have a few more events to play, so that'll be good.'
McKenzie was also seeking his first win and mixed three birdies with two bogeys on the outward half to fall four shots off the pace heading to the back nine.
The Australian reached the green in two at the par-5 11th, but missed the eagle try. McKenzie tapped in for birdie, but redeemed himself a few holes later when he bogeyed the par-5 15th to put the pressure on Hearn.
McKenzie could not sustain his momentum, however, and bogeyed the par-3 17th to finish one shot off the pace.
Charles Warren, a two-time winner on the Nationwide Tour this year, carded a 70 to join Jim Rutledge and Kevin Johnson in a tie for fifth place at 9-under-par 279.
Paul Gow, Jason Buha, John Morse, Jason Schultz and Jon Mills shared eighth place at 8-under-par 280.