Montero converted a penalty kick in the 41st minute and then scored again in the 78th minute for his first multi-goal game since July 29, 2017, at FC Dallas. The veteran forward now has 70 career goals in MLS regular-season play.
The Impact played the majority of the game with only 10 men after defender Rudy Camacho was issued a straight red card in the 37th minute.
After Camacho was taken down by Cristian Dajome, Camacho retaliated by striking Montero in the leg as Montero was checking on his opponent. Since the blatant foul occurred within the Impact's box, the Whitecaps were awarded the penalty kick that Montero buried for the opening score.
Vancouver struck again on a well-built passing play in the 44th minute. The Whitecaps moved the ball down the left side of the field, resulting in David Milinkovic crossing to Dajome for Dajome's team-leading third goal of the season.
The Whitecaps have scored eight goals over their last three games. This offensive surge has come after a five-game stretch that saw Vancouver endure four shutout losses.
Romell Quioto scored Montreal's lone goal of the game. In the 70th minute, the striker got the ball in the box and found enough space to turn and shoot, despite close marking from defender Ranko Veselinovic.
It was Quioto's fifth goal of the season, and his third goal in as many games against Vancouver.
After a 4-2 loss to the Impact on Sunday, the Whitecaps made six changes to their starting lineup and played a much sharper defensive game on Wednesday. Montreal only had four shots on goal against Whitecaps goalie Thomas Hasal, who made a pair of big saves during an Impact rally in the first half.
A victory would have clinched the Impact a berth in the Canadian Championship final. Instead, Toronto FC will advance to face the Canadian Premier League winner for a berth in the 2021 CONCACAF Champions League. In games between MLS' three Canadian clubs, TFC went 4-2-0, Montreal finished 3-3-0, and Vancouver posted a 2-4-0 mark.