Guay, of Mont-Tremblant, Que., posted a time of one minute 5.84 seconds to finish just .11 seconds behind third-place finisher Travis Ganong of the U.S. Guay has been a model of consistency of late, posting a third straight top-five effort in a World Cup event.
He was 10th in the downhill event at the Sochi Games.
Olympic super-G champion Kjetil Jansrud and Austrian Georg Streitberger finished atop the leaderboard. With poor visibility due to rain and fog, Jansrud and Streitberger clocked 1:05.72 on the Olympiabakken course.
"Sharing or not sharing, it's still a win. It's a cool thing," Jansrud said. "One minute and five seconds and you manage to go inside the same hundredth, it's pretty exciting."
Although Jansrud found the conditions "very difficult" he praised the organizers for preparing the course well.
"They couldn't have done a better job," he said. "There was a little rain on the goggles, which made it a little hard to see and it was rattling underfoot."
Vancouver’s Manuel Osborne-Paradis was 25th while Jeffrey Frisch of Mont-Tremblant, Quebec was 28th. Calgary’s Jan Hudec, the bronze medallist in the Olympic Super-G, was 44th.
It was a second career World Cup win for Jansrud, who took gold in the super-G and earned a bronze in downhill at the Sochi Olympics. For Streitberger, who had only one previous podium finish, it was a first victory at age 32.
"It's awesome to be first with Kjetil," said Streitberger, who was the first to go down the slope. "I didn't want to start this day seeing the fog and the snow, but now it's perfect."
Ganong finished .12 behind in third for his first podium finish, continuing his good late-season form after an impressive fifth-place finish in the downhill at the Olympics. His previous best in a World Cup race was seventh, twice.
"I'm obviously happy we raced today. It was foggy with pretty soft snow, but the conditions were really challenging," Ganong said. "It was a World Cup-calibre race, the terrain was bumpy and the snow was variable. You had to push and ski well to win."
Ganong was the eighth racer to start and, with rain blurring his vision, his hands became like windscreen wipers.
"I had to do a goggle wipe halfway down the hill," he said. "But on days like today you've just got to forget about the weather and just ski. You can't really see anything, so you just have to put your head down."
Erik Guay of Canada was fourth, .23 behind.
The last time two men shared a win was in December 2012, when Dominik Paris of Italy and Hannes Reichelt of Austria beat Aksel Lund Svindal of Norway by .01.
"I'm just excited I was not one hundredth behind," Jansrud said, laughing.
There was tie at the Olympics with Tina Maze of Slovenia sharing the women's downhill gold medal with Dominique Gisin of Switzerland.
Jansrud has 13 career podiums, four of those in Kvitfjell.
Two years ago, he was on the podium for three straight days: Winning a super-G, finishing second in downhill and third in another super-G. He could repeat that hat trick this year, with a downhill set for Saturday and a super-G on Sunday.
"I think I have great chances," he said. "I grew up on this hill and we'll see; another day, another possibility."
Svindal finished fifth on Friday, .37 adrift, and was again upstaged by Jansrud.
Svindal is looking to bounce back from a disappointing Olympics, where the two-time overall World Cup champion finished fourth in the downhill, eighth in the super-combined and seventh in the super-G.
However, he closed the gap on overall World Cup leader Marcel Hirscher to 13 points and extended his lead in the downhill standings to 125 over Reichelt, who is sidelined after back surgery. Jansrud is level third overall in downhill with Switzerland's Patrick Kueng, who was 12th on Friday.
Italy's Christof Innerhofer — a silver medallist in downhill at Sochi — thinks the race should have been called off. He finished 14th.
"I think it's bad to race with these conditions, because I don't think it's good PR, for the ski World Cup," Innerhofer said. "The snow is dead, you feel nothing. You cannot (make) the difference here. There's almost no turns, no difficult turns, (you) can't push really hard."