Guay, from Mont-Tremblant, Que., found the quickest line through the modified Beaver Creek course, finishing in one minute 43.48 seconds. Florian Scheiber of Austria was second and Peter Fill of Italy third on a clear but cold afternoon.
Travis Ganong had the top time for the U.S., 0.55 seconds behind Guay. Bode Miller was 66th as he returns from a knee injury that kept him out all of last season.
The downhill race is Friday.
This was the first chance the skiers had to try out the revamped course after the training session was cancelled Wednesday when a snowstorm hit the area. Training also was postponed Tuesday because of travel issues for some teams.