Playing the back nine first on a brilliant sunny day at Glen Abbey Golf Club, Steele mixed eight birdies with a single bogey for a one-shot lead over compatriots Matt Kuchar and Scott Brown and Australian Scott Gardiner.
Steele had three birdies on his outward nine on the Jack Nicklaus-designed layout and picked up the pace after the turn with five birdies over seven holes before dropping his only shot of the day at the ninth.
Kuchar, the highest ranked player in the field at world number six, mixed an eagle with five birdies and a bogey while Brown turned in a flawless round with six birdies.
"It was perfect conditions," smiled Kuchar, who has made 20 consecutive cuts, including all 16 starts this season. "I feel like last week, conditions were so challenging and so difficult at the British Open to come here and play golf that is more friendly and more what we are use to was great."
Gardiner, who has made the cut just twice in his last 16 events, opened his round with a par before reeling off six consecutive birdies to race up the leaderboard.
The Australian's red-hot start cooled with seven consecutive pars before he picked up another birdie at 15 followed by his only bogey of the day at 16.