Dave Christensen, David Faught, Rob McMillan, Drew Scott and former U.S. Amateur champion Hank Kuehne are tied for fourth place at 4-under-par 68.
Barber flew out of the gate Thursday with five birdies in his first six holes. He dropped a pair of shots with bogeys at 10 and 11, but birdies at three of his final six holes drew him into a share of first place.
Barber is the reigning Order of Merit champion on the Canadian Tour and with five top-10s in his last five starts, the 29-year-old could be poised to make another run to the top.
'I've been putting consistently, so when I have a good ball-striking round like today, I can take it low,' said Barber. 'But we have a tough field here, everyone is back for this event. I just need to keep things in focus and hopefully it all works out.'
McGuigan is one day removed from celebrating his 32nd birthday and with seven birdies and one bogey in his round, the celebration might last longer than expected.
'I've been in this position a few times, and if you start planning victory parties, you'll get slapped in the face in a hurry,' he said. 'I'll wait until Sunday and see where I am. If there's one thing I'm learning as I get older, it is not to force things.'
Parker was working on a bogey-free round Thursday until he dropped a shot at the par-3 15th hole. He rebounded with a pair of birdies in his remaining three holes to get his piece of the lead.
Brett Bingham, Matt Daniel, Brad Fritsch, Mike Grob, Scott Gutschewski, Chris Learmouth, Rich Massey, David McKenzie and Bryn Parry share ninth place at 3-under-par.
Defending champion Paul Devenport carded a 1-under-par 71 and is tied for 35th.
Full-field scores from the Telus Quebec Open