A police source tells the Associated Press the remains appear to be a human head.
Magnotta is accused of the murder and dismemberment of Concordia University student Jun Lin. He has pleaded not guilty and has opted for a trial in front of a jury.
Lin's torso was discovered stuffed in a suitcase behind Magnotta's apartment building in late May. His hands and feet were mailed to political parties in Ottawa and two B.C. schools.
His head has still not been found.
Montreal Police spokeswoman Anie Lemieux says tests will be run on the remains to determine if they are in fact body parts and whether they're related to the Magnotta case.
"For the time being it is still too early to confirm anything," Lemieux said.
Montreal's Major Crime Squad cordoned off parts of the Angrignon Park in the city's west end after the discovery was made following a tip on Sunday.
Magnotta, 29, is accused of the first-degree murder of Lin, along with defiling his corpse. He is also charged with harassing Prime Minister Stephen Harper and MPs, and publishing and mailing obscene material.
He was arrested in Germany after an international manhunt ended with his capture at a Berlin Internet cafe.
The amateur porn actor will face a preliminary hearing next March where part of the evidence against him will be heard.
Thirty-three-year-old Lin, who was originally from China, was studying computer science in Montreal.
His family travelled to Canada to receive his remains and have been following Magnotta's legal proceedings.
— with files from the Associated Press