McIlroy, making his first appearance at the event in Ontario, is trying to bounce back after failing to make the cut at the Memorial tournament in Ohio last week, his first missed cut of the season.
The 30-year-old Northern Irishman used his weekend off working on his game and said the extra practice has paid off.
"I feel like I turned that missed cut into a positive," he said. "There were a couple things in my game that were highlighted and I had a chance to work on them ... that's why I am where I am on the leaderboard."
McIlroy had the shot of the day on the par-four 15th when his approach shot from 130 yards away narrowly missed the cup, setting up a 10-inch birdie putt.
Veteran Kuchar, who was also a co-leader after his second round, said he will need to step up his game if he is to win his first Canadian Open trophy.
"The goal is to just keep making improvements," said Kuchar, who mixed three birdies with two bogeys on Saturday.
"Tomorrow I need a firmer understanding of the greens so I can roll in more birdies."
American Brandt Snedeker, who produced a sparkling 10-under-par 60 in Friday's second round, shot 69 on Saturday that put him in a three-way tie in fourth on 12-under with Canada's Adam Hadwin and Ireland's Shane Lowry.
Snedeker's best moment came on 15 when he sank a 52-yard putt for his third birdie of the day, although he followed it up with his second bogey on the next hole.
Defending champion Dustin Johnson finished his third round with four birdies and two bogeys and is tied for 17th at six-under.
(Reporting by Rory Carroll; Editing by Greg Stutchbury)
