[1] He also competed for Canada 19 times, winning multiple medals highlighted by gold at the 2007 Pan American Championships in Men's Doubles with François Viens.

[3] Gagnon won the National Team Doubles Selection Event in 2001 with Francis Guillemette by defeating Kris Odegard and Ryan Powell in the final.

[5] Gagnon and Francis Guillemette finished 5th at the 2002 National Team Doubles Selection Event in Saskatoon, Saskatchewan, as they lost to Mike Ceresia and Corey Osborne in the quarterfinals.

Gagnon and Francis Guillemette finished 4th at the 2003 National Team Doubles Selection Event in Saskatoon, Saskatchewan, where they lost to Corey Osborne and François Viens in the semi-finals, and then dropped the 3rd place match versus Mike Green and Tom O’Brien.

[6] Gagnon and Francis Guillemette finished 7th at the 2004 National Team Doubles Selection Event in Saskatoon, Saskatchewan, as they lost in the quarterfinals to Mike McPhee and Bill Shepley, 13–15, 15–9, 11–6.

In the Singles Selection Event in Brossard, Québec, Gagnon lost to Brian Istace in the semi-finals, but won the 3rd place match against Corey Osborne, 15–4, 10–15, 11–1.

At the 2006 National Team Doubles Selection Event in Calgary, Gagnon and François Viens finished 3rd behind Mike Green and Brian Istace in 1st and Francis Guillemette and Kris Odegard in 2nd.

He and François Viens were runners up in Men's Doubles, as they beat Francis Guillemette and Kris Odegard in the semi-finals, 18–16, 11–15, 11–8, but lost in the final to Mike Green and Brian Istace, 15–7, 15–10.

At the 2007 National Team Doubles Selection Event in Victoria, British Columbia, Gagnon and François Viens finished 2nd after losing to Mike Green and Brian Istace, 15–10, 15–10.

But in Brossard, Québec Gagnon won the Singles Selection Event for the first time in 2007, when he defeated Green, Kris Odegard and Viens in the final four playoff round.

[17] In the National Team Doubles Selection Event in Windsor, Ontario, Gagnon and François Viens finished 2nd behind Green and Brian Istace, who defeated them 15–11, 15–12, in the final four playoff.

[23] In that tournament, Gagnon defeated Daniel Maggi of Argentina in the Round of 16, then Fernando Rios of Ecuador in the quarterfinals, but lost to Jack Huczek of the US in the semi-finals, 3–15, 15–8, 11–7, which put him in the bronze medal match.

[34] At the 2010 Canadian Championships in Burnaby, British Columbia, Gagnon finished 3rd, as he lost in the semi-finals to Mike Green, 15–9, 15–12, but then won the 3rd place match against Kris Odegard, 15–10, 15–1.

Gagnon won the first National Team Selection Event of 2010–11 in Edmonton by defeating Tim Landeryou in the semi-finals, 8–15, 15–13, 11–3, and his former doubles partner Francis Guillemette in the final, 15–8, 15–3.

[38] Gagnon competed in the 2011 Pan American Championships in Mangua, Nicaragua, where he reached the semi-finals with a win over then defending champion Ricardo Monroy of Bolivia, 5–15, 15–14, 11–5.

[41] Gagnon competed at the Pan American Games for the first time in 2011 in Guadalajara, Mexico, where he earned bronze in Men's singles by defeating Luis Pérez of the Dominican Republic, 15–7, 15–9, in the quarterfinals, but losing to Mexican Gilberto Meija, 11–15, 15–14, 11–5, in the semi-finals.

In 2012 in Brossard, Québec, Gagnon and François Viens won Men's Doubles for the 3rd time at the Canadian Championships, by defeating Pedro Castro and Eric Desrochers in the final, 15–8, 8–15, 11–9.

[46] Gagnon partnered with Mike Green to play Men's Doubles at the 2012 World Championships in Santo Domingo, Dominican Republic, where they lost in the quarterfinals to Bolivians Roland Keller and Ricardo Monroy, 15–10, 15–11.

But in the Men's Team competition Canada defeated Ecuador in the quarterfinals, Mexico in the semi-finals, before losing to the US in the final, so Gagnon came home with a silver medal from that event.

[54] Gagnon played Men's Doubles with Mike Green at the 2015 Pan American Championships in Santo Domingo, Dominican Republic, where they lost in the quarterfinals to Costa Ricans, Felipe Camacho and Teobaldo Fumero, 2–15, 15–11, 11–8.

[55] In Burnaby, British Columbia, Gagnon was 3rd in singles at the 2015 Canadian Championships, as he lost in the semi-finals to Samuel Murray, 15–10, 15–10,[56] and then got a default win from Mike Green.

They defeated Argentina's Daniel Maggi and Shai Mazuri in the quarterfinals, but lost to Bolivians Roland Keller and Conrado Moscoso, 15–9, 15–11, in the semi-finals, resulting in bronze medals for them.

[58] Gagnon captured a second bronze medal in Toronto, as Canada defeated the Dominican Republic in the quarterfinals, but lost to the US in the semi-finals of the Men's Team event.

Gagnon competed with Team Canada 19 times,[59] winning 16 medals, including gold in Men's Doubles with François Viens at the 2007 Pan American Racquetball Championships.

Gagnon was featured in one of CNN's sports photos of the year, as he was photographed jumping in the air to avoid a shot by Jose Rojas of the USA during their doubles match at the 2015 Pan American Games.