Rob Oppenheim is alone in third place after a round of 5-under 67, while defending champion Stuart Anderson is one stroke further back in a tie for fourth place with four other players.
Anderson's round included his first career hole-in-one in competition, an ace at the par-3, 156-yard eighth hole.
'Like any other day, you feel like you leave a few out there,' he said. 'But any time you shoot 68 with a hole-in-one, you can't complain.'
Also at minus-4 are Lee Curry, Brendan Steele, Brian Guetz and Ron Harvey, Jr.
Yi was flawless on his way to a share of the lead, opening the fourth official Canadian Tour event with a bogey-free round.
'I just played a solid round of golf,' said Yi. 'I would make a bunch of pars and then sneak a birdie in. It was a clean round from start to finish.'
Friesen had one more birdie than Yi, but dropped a shot at the par-4 13th. His round included a run of three straight birdies from the 15th.
Sharing ninth place at minus-3 are Derek Gillespie, Rob McMillan, Ben Pettitt, Stephen Gangluff, Eugene Smith, Ryan Vallely, Travis Johnson, Matt Daniel and Eddie Heinen.