The newspaper reported that police obtained at least two dozen court-approved surveillance warrants in 2016.
Those warrants allowed them to know who journalist Patrick Lagace called and texted and gave them access to his location through the phone's GPS.
Montreal Mayor Denis Coderre called the spying "worrisome" and "unacceptable".
The surveillance was part of an internal probe into allegations that Montreal police had fabricated evidence in gang and drug investigations.
Two officers were charged this summer as a result of the internal investigation.
Revelations that police had been monitoring Mr Lagace's phone shocked Canadian media and free speech advocates.
La Presse deputy managing editor Eric Trottier said the surveillance was an "unequivocal attack against the institution of La Presse and against the entire journalistic profession".
"One must protect the freedom of the press," he said.
"Are you a journalist? The police spying on you specifically to ID your sources isn't a hypothetical. This is today," tweeted whistleblower Edward Snowden.
Montreal Police Chief Philippe Pichet said the surveillance was necessary given the "exceptional situation" and that the investigation targeted one of the department's own officers, and not Mr Lagace.
"We are very conscientious about the importance of respecting the freedom of the press. However, the SPVM (Montreal police department) also has the responsibility to carry out investigations on criminal acts - even against police officers," he said during a news conference.
Speaking to the CBC, Mr Lagace said he was "flabbergasted."
"I lived in this fiction that this could not happen in this country," he said.
Montreal police spied on a La Presse journalist for months to try to learn who his sources were, the newspaper reported on Monday.