World champion Rui Costa (Lampre-Merida) was second and Tony Gallopin (Lotto-Belisol) third.
"I couldn't have asked any more of the team again today," said Gerrans. "We set out a plan at the start of the day, everyone followed it perfectly and the race unfolded exactly as we wanted.
"To still have four or five teammates there coming into the final was amazing, so I am just really happy to be able to finish off some great teamwork again."
Coming two days after the Quebec race, Montreal did not offer the same beautiful weather as the first event, with riders facing grey skies and temperatures barely out of the single digits Celsius.
Montreal is a classic course, with major events running back 40 years, when Eddy Merckx won a world title. He subsequently stated that Montreal was his toughest Worlds.
The circuit is dominated by the Mont Royal climb of nearly three kilometres, early in the 12km lap. The riders immediately descend the other side and head through a series of left and right turns on city streets before a second shorter but steeper climb and a fast descent.
The route then curves around the base of Mont Royal before heading down a boulevard past the finish line and making a 180-degree turn for the final 400 metres of slight uphill to the finish line. The riders had to cover 17 laps for a total of 205.7 kilometres.
Four riders went away on the first lap. First Arnold Jeannesson (FDJ), Louis Vervaeke (Lotto-Belisol) and Jan Polanc (Lampre-Merida), who were then joined by Ryan Roth (Team Canada). At the beginning of the second lap the gap was two minutes, but it quickly zoomed over ten minutes, with the peloton disinclined to chase.
As the time gap went into the double digits, the World Tour teams began to take notice, and started sending riders to the front to bring the break back. However, their efforts were ineffective for the first half of the race, before Astana sent most of their team to the front to work for Enrico Gasparotto.
Finally, the break started to come back, as the laps piled up and the break began to tire. Roth was the first to go, with three laps remaining, and he was quickly joined by Jeannesson. Polanc and Vervaeke kept going, with the gap two minutes at two laps to go. Vervaeke took the final KoM points to win that competition then dropped off, leaving Polanc alone at the front. The Lampre rider began the final lap with a lead of about a minute, but was swallowed up on the Mont Royal climb.
The attacks began on that climb, with a group of nine going over the top clear, including Gerrans and world champion Costa. However, it was reabsorbed by the quickly shrinking lead group. Costa made another solo
effort with three kilometres to go, but Orica GreenEDGE was firmly in control, setting up a train for Gerrans in the final two kilometres.
Peter Weening led Gerrans out of the final U-turn and onto the finishing stretch, where Gerrans exploded off his wheel to finish nearly five bike lengths ahead of the bunch.
"I have worked pretty hard after the Tour de France and just tried to maintain things for the last few weeks leading into these races," said Gerrans. "Hopefully I still have a little bit to find before the world championships in a couple of weeks."
Grand Prix du Montreal: 205.7 km, Montreal
1 Simon Gerrans (AUS) Orica-GreenEDGE 5hr 24min 27sec
2 Rui Costa (POR) Lampre-Merida
3 Tony Gallopin (FRA) Lotto-Belisol
4 Ramunas Navardauskas (LTU) Garmin-Sharp
5 Romain Bardet (FRA) AG2R
6 Tom Dumoulin (NED) Giant-Shimano
7 Greg van Avermaet (BEL) BMC
8 Jonathan Hivert (FRA) Belkin
9 Enrico Gasparotto (ITA) Astana
10 Bauke Mollema (NED) Belkin