The 44-year-old Furyk, the 2006 winner at Hamilton and 2007 champion at Angus Glen, matched Petrovic at 10-under 130 on the tree-line Blue Course.
"Winning any event is special," Furyk said. "I've had a lot of success (in Canada) and really a lot of support here. But we're only at the halfway point."
The 47-year-old Petrovic followed his opening 64 with a 66. He missed the cuts in his last five events.
"I have been hitting the ball really well for about the last three weeks," Petrovic said. "I've seen signs of some good rounds coming. Am I surprised? Maybe a little."
Canada's Graham DeLaet, playing in a threesome with Furyk and Matt Kuchar, was two strokes back along with Kyle Stanley. DeLaet, trying to become the first Canadian winner in the event in 60 years, also had a 63.
"They're fun to play golf with," Furyk said about DeLaet and Kuchar. "We chatted a lot out there. And then to have everyone play well, you're seeing birdie putts going in, it's a lot of fun. And I think you can feed off that a little bit. Those guys are making birdies, you feel like putts are going in, it's a good vibe."
Stanley shot 67.
The 32-year-old DeLaet, winless on the PGA Tour, had nine birdies and two bogeys.
"I felt I was in control of my game all day, with a couple of little hiccups," said DeLaet, from Weyburn, Saskatchewan. "I mean, all three of us played great. I never saw so many putts rolling in. It was a lot of fun. We were feeding off each other. When you see putts rolling in from everywhere like it was in our group, you just feel like putting's easy or something and you just start holing them."
Pat Fletcher, born in England, was the last Canadian winner, taking the 1954 event at Point Grey in Vancouver. Carl Keffer is the only Canadian-born champion, winning in 1909 and 1914. Albert Murray, a Canadian also born in England, won in 1908 and 1913.
Furyk and DeLaet matched the course record set by David Morland and Scott Verplank in the second round of the 2001 Canadian Open. Verplank went on to win that week.
"To share a course record here is pretty special and to have two guys in one group do it is pretty amazing," DeLaet said.
Furyk, coming off a fourth-place finish in the British Open, made four straight birdies on Nos. 11-14 on his opening nine on the rain-softened course and added birdies on Nos. 1, 6 and 8.
"The golf course is soft and receptive, and they have it set up where we can attack and fire at pins, so scores are going to be good," Furyk said. "It would be a totally different scenario if these greens were firm."
He won the last of his 16 PGA Tour titles in 2010.
Petrovic was the last player to get in the field, grabbing a spot when Benjamin Alvarado withdrew Tuesday. Petrovic won his lone PGA Tour title in New Orleans in 2005.
Michael Putnam, tied for the first-round lead with Petrovic, was 6 under after a 70. Kuchar also was 6 under after a 65.
Taylor Pendrith, the 23-year-old Canadian amateur, had a 75 after opening with a 65.
"It was a disappointing round," said Pendrith, who had a double-bogey, four bogeys and one birdie. "To play well yesterday and come out and not play my best, I didn't hit many greens -- only six -- and didn't give myself too many chances for birdies. My short game was pretty good -- I had a few nice saves -- so I can't be too disappointed about that. The ball-striking was off today."