Piercy, who shot a course-record 62 in the opening round at the Hamilton Golf and Country Club, returned a three-under-par 67 for an 11-under 129 while McGirt joined the overnight leader with a four-under 66.
The duo were one shot clear of American Robert Garrigus (66), who is alone in third at 130 while compatriot Bo Van Pelt (66) was a further shot back.
"It's kind of a boring 67 to be honest," said Piercy.
"There was not a lot of excitement like yesterday. I made a putt or two for birdie, made a couple of nice par saves.
"I wasn't really in a whole lot of trouble most of the day and it was solid overall."
Former world number one and 2004 Canadian Open champion Vijay Singh, who started on the back nine, bogeyed two of his first four holes and made five consecutive birdies from the par-four third, his 12th, for a three-under 67 that left him three shots back of the leaders.
South African Tim Clark (62), who equalled the course record set by Piercy on Thursday, and American Josh Teater (65) were tied with Singh in fifth place.
Clark, who started the day eight shots off the pace, was flawless as he carded six birdies and holed out for an eagle on the par-four second.
Piercy looked set to go low again when he claimed back-to-back birdies on the fourth and fifth holes but a bogey on the eighth and some regulation pars kept him in check.
McGirt was also on track to attack the new record when he was four under through eight holes but managed just one more birdie in his last 10 and also picked up a bogey.
Els, fresh off his Open triumph on Sunday, offset four bogeys with four birdies for an even-par 70 but his two-day 142 total left him three shots outside the cut.
Two-time Canadian Open winner Jim Furyk (70) and defending champion Sean O'Hair (72) also missed the cut.
David Hearn, hoping to become the first homegrown tournament winner since 1954, was the top Canadian in the field at 136, seven shots adrift. He was just one of five Canadians to make the cut.
- Hamilton Golf and Country Club