The 31-year-old Monteith, who played the character Finn Hudson on the TV series about a high school glee club, was found dead in his room on the 21st floor of the Fairmont Pacific Rim Hotel on Vancouver's waterfront at about noon Saturday.
Deputy Police Chief Doug Lepard says there is no indication of foul play. Monteith's body was found by hotel staff after he missed his check-out time, Lepard said.
"We do not have a great deal of information as to cause of death," said Coroner Lisa Lapointe.
Lepard said Monteith had been out with people earlier and that those people are being interviewed.
Monteith had voluntarily entered rehab for substance abuse problems in April.
When he admitted himself to the treatment facility in April he had asked for privacy as he took steps toward recovery, a representative said at the time.
Lea Michele, his Glee co-star and real-life girlfriend, told People magazine that she loved and supported Monteith and was proud he was seeking help.
It was not Monteith's first time in rehab. He received treatment when he was 19 and had previously talked about his addiction struggles, saying he had a serious problem and took just "anything and everything."
He told Parade in 2011 that he was "lucky to be alive."
Michele played his on-air girlfriend in "Glee" - Rachel Berry.
The show, with its pop music-based musical numbers and high-profile guest stars including Gwyneth Paltrow, became an immediate hit and made stars of its relatively unknown cast.
On his Twitter account, Monteith described himself as "tall, awkward, canadian, actor, drummer, person."
