Polls opened at 10 a.m. ET on Sunday to elect a replacement for Marie Calderone, who resigned from her position in June.
Calderone was a member of Union Montréal, the former Montreal mayor's party.
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Amid the high tension at city council, the partial election is considered to be a test for the three parties.
On Tuesday, Gérald Tremblay stepped down from his position as mayor after being accused of taking kickbacks during a testimony at the province's corruption inquiry.
Friday, Michael Applebaum, chair of the city's executive committee, stepped down from his role claiming his colleagues had hidden a report about price inflations on public works projects.
Leader of Projet Montréal Richard Bergeron said "what we need now is to regain the trust of Montrealers. The byelection in Rivière-des-Prairies could be an important turn."
Louise Harel, leader of Vision Montréal, announced Saturday she would deposit a formal request for the said "hidden" document before the access to information commission.
Nino Colavecchio of Union Montréal, Cindy Leclerc of Vision Montréal and Nathalie Pierre-Antoine of Projet Montréal are running for election in the district.
Polling stations close at 8 p.m.