Guay was born in Montreal and starts for the Mont-Tremblant ski club . He drove his first FIS races in January 2002 , achieved top 10 results from the start and podium places for the first time next winter. From January 2003 Guay also took part in races of the Nor-Am Cup , in 2004 he was accepted into the Canadian national team. After several top 10 results, he reached his first podium in the Nor-Am Cup towards the end of the 2004/05 season when he was third in the Super-G of Le Massif . Three weeks earlier he had won the bronze medal in giant slalom at the Junior World Championships in 2005 in Bardonecchia, Italy . At his third and final Junior World Championship, in 2006 in the province of Québec , Guay was the host country's only medalist with gold in giant slalom and bronze in downhill. In the 2005/06 Nor-Am season he reached three podium places and fourth place in the giant slalom discipline. In addition, he came to his first three appearances in the World Cup in the same year , in which he did not see the goal.
On November 26th, 2006, Guay won his first World Cup points with 25th place in the Super-G of Lake Louise - which were also his only ones. A week and a half later he celebrated his first two victories in the Nor-Am Cup when he again won two runs in Lake Louise. On December 13, 2006, however, the season was over for him. Guay fell during downhill training on the Saslong in Val Gardena and suffered serious injuries in his right knee. He also had to take a break throughout the next winter and was only able to take part in racing again in the 2008/2009 season, but was still impaired by knee problems. After three World Cup races without any points at the beginning of winter, he was used in the Nor-Am Cup until the end of the season, where he achieved a total of six podium places in 2008/09 and won this discipline classification with two super-G victories. Because of the persistent knee problems, Guay underwent a meniscus transplant in the summer of 2009 , after which he did not take part in competitions.
Guay has worked as a coach since the end of his active career. He initially worked for the ski team at Westminster College in Salt Lake City and was accepted into the coaching team of the Downhill / Super-G group of the Canadian Ski Association in 2012.