Guetz was joined atop the leaderboard by Erik Compton, who owns three Canadian Tour wins.
The round was suspended due to darkness with three players left on the course. Those three will return to Brookside Country Club at 10:00 a.m. (ET) to complete their rounds. The start of the second round will not be effected.
Scott Gibson and Ron Harvey, Jr. are one stroke further back at minus-7. Dan Swanson posted a 6-under-par 66 and shares fifth place with Scott McNeil, David F. Walker and John Mallinger.
Guetz started on the back nine and opened with a birdie. He holed out for eagle on the 13th when his approach shot from 104 yards out dropped into the hole.
Three holes later, Guetz drained an eagle at the par-5 15th as he ran home a 25-foot putt. The 26-year-old also played the front side at 4 under to share the lead.
'Usually you are pretty happy with two eagles in a week, never mind the same nine,' said Guetz, who needed only 11 putts on his first nine. 'The conditions were absolutely perfect for us.'
Compton is looking to regain his form from 2004, when he was the tour's leading money winner and collected two of his three wins.
Ricky Barnes, the 2002 U.S. Amateur champion, opened with a 5-under-par 67. He shares ninth place with Christopher Baryla, 2000 U.S. Amateur champion Jeff Quinney, Michael Walton, Darren Griff, Matt Hansen and Keith Huber. Thirteen more players are a stroke further back at minus-4.