For Henry, it was his first win on the PGA TOUR and it came with relative ease. He led by as many as five during the final round, but two back-nine bogeys dropped his final margin to three.
Australian Nathan Green used a 4-under 66 Sunday to take fourth place at minus-9.
Henry led by two entering the final round. A birdie on the third extended the cushion to three.
Moore cut the lead to two as he birdied the fourth. A bogey on five dropped Moore back to minus-8, but he quickly atoned for that error with a birdie on the sixth at the TPC at River Highlands.
Henry parred four straight from the fourth to remain at 12 under. He started to stretch his lead with a birdie on the par-3 eighth.
The 31-year-old made it two in a row at the ninth to move his lead to five over Moore. Both Henry and Moore, who were playing one group apart, birdied the par-3 11th.
Henry gave a stroke back at the 12th, but erased that mistake with a birdie on 14. Henry dropped a stroke on the par-4 17th to slip to minus-14, but he parred the last to win by three.
Moore carded a birdie on 15, but still was four back. He tripped to a bogey on 16, but a birdie at the last assured Moore of a tie for second. He also shared second last year at the Bell Canadian Open.
Mahan, who was one group behind Moore, got to 6 under with birdies on one and four. He faltered to a bogey at the par-5 sixth, but came right back with birdies on seven and eight.
The 24-year-old tripped to another bogey on the 10th. Mahan recovered that lost stroke with a birdie on 13. He closed with back-to-back birdies from the 17th to join Moore in second. For Mahan, it was also the second time he shared second place. He first did that at the 2004 Reno-Tahoe Open.
Two-time U.S. Ryder Cupper Stewart Cink closed with a 3-under 67 to finish at 7-under-par 273. He shared fifth place with Woody Austin (68), Bubba Dickerson (67) and Shigeki Maruyama (66).
Notah Begay III, Steve Flesch, Skip Kendall, Peter Lonard, David McKenzie, Joe Ogilvie and Nick Watney shared ninth one stroke further back at minus-6.