Gosselin was a former brother-in-law of a reputed high-ranking Mafia figure in Montreal, Raynald Desjardins.
Police say the four men arrested Wednesday morning are all known street-gang members.
They are Edrick Anthony, 34, Olivier Guay, 30, Standley Minuty, 29, and Kevin Tate, 29.
Montreal police Cmdr. Ian Lafrenière said police do not believe the suspects were acting on their own.
"We got all the reasons to believe … they've done that for the Mafia," Lafrenière said.
Desjardins, known as Vito Rizzuto's right-hand man, has been charged in the murder of another Mafia boss, Salvatore Montagna, in 2011 and is awaiting trial for first-degree murder.
Gosselin was gunned down outside his home, as he was getting out of his car, at the corner of Jean Tavernier and Pierre Gaulin Streets. His homicide was the 5th of 2013 in the Montreal region.
Police say they are looking for witnesses who might have seen a navy blue 2002 Chrysler Caravan or a beige or gold 2000 Mazda Protégé around the time of the shooting.
Police are asking anyone with information about the case to contact Info-Crime at (514) 393-1133.