The 31-year-old world number 309 birdied the first two holes and two of the last three to reach seven under with US Open champion Dustin Johnson.
World number one Jason Day had six bogeys in a 76 and is eight shots back.
The cut came at two over, one too many for England's Matthew Fitzpatrick, while Northern Irishman Graeme McDowell finished seven over after a 76.
Johnson, the world number two who shared the overnight lead with List after an opening 66, had an early tee time on another hot, dry day at the Glen Abbey Golf Club.
He started at the 10th hole and bogeyed the 11th, double-bogeyed 12 and bogeyed the par-five 13th but later compiled six birdies in nine holes in his 71.
"The wind today almost feels like it's a little bit heavier and it's affecting the ball a little bit more, and it's a little bit different direction," said the long-hitting American, who was tied for ninth at last week's Open Championship.
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List, who dropped three shots in four holes midway through his round, is in his ninth season on the PGA Tour and has yet to record a victory, but has secured two top-10 finishes this year.
Two birdies at the par fives towards the end of the round kept him in contention and he said: "I'm real happy the way I finished up."
Johnson and List have a one-shot advantage over a group of three including amateur Jared du Toit, bidding to become the first Canadian to win the event since 1954.
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American Luke List carded a 71 to retain a share of the lead after round two of the Canadian Open in Ontario.