The final round, which will resume Monday at 8 a.m. ET (1300 GMT), was interrupted by inclement weather and the nearly four-hour delay prevented all but 27 players from finishing their rounds.
McDowell, who started the day three shots behind overnight leader Derek Fathauer, picked up three strokes with a string of birdies starting at the par-five fifth hole.
The 2010 U.S. Open champion maintained that form on the back nine where he birdied the 10th, 12th and 13th holes before being forced off the course with a 19-under total of 200.
Knox, who triumphed in his World Golf Championship debut in Shanghai, was red-hot on the front nine where he made four consecutive birdies from the par-four third hole before picking up another shot at the eighth and 11th holes.
American Jason Bohn was two shots behind the leaders with six holes to play while compatriot Fathauer was at 15-under for the tournament with six holes to play.
(Reporting by Frank Pingue in Toronto; Editing by Greg Stutchbury)
