Police said two boaters spotted the suitcase about 2.5 kilometres from shore near Bluffers Park, in the city's east-end on Wednesday morning.
The boaters towed the suitcase to shore and contacted authorities, who searched the waters in the area but found nothing further. The coroner was brought in and conducted an initial investigation.
"The coroner has determined at this time the contents of that suitcase to be that of human remains, to be specific, that of a badly decomposed torso," said Toronto police Det. Les Dunkley.
An autopsy has been ordered for Thursday, after which police said they would have more information to share with the public.
"Until we get the results of that post-mortem examination, Toronto police is treating this as a suspicious death investigation," Dunkley said.
Police wouldn't say if the torso found on Wednesday was connected to the murder of Guang Hua Liu, but Dunkley added that Toronto police have been in touch with Peel Region authorities, who had been leading the investigation into her death.
Parts of the 41-year-old woman's body — but not her torso — were found in mid-August scattered west of Toronto and near her home in the city.
Liu's estranged boyfriend, Chun Qi Jiang, 40, was arrested Aug. 26 and charged with second-degree murder in what police say was a domestic-related homicide.
Liu was reported missing on Aug. 11, one day after her friends dropped her off in front of a now-defunct spa she owned called the Forget Me Not Health Centre in east Toronto.
On Aug. 15, her right foot was found in the Credit River in Mississauga, Ont., about 45 kilometres west of her home.
Liu's head and hands were later discovered in the same river in the Hewick Meadows Park area.
Days later, two calves, a thigh and an arm were found in West Highland Creek, just blocks from where she lived.
Forensic tests determined all the remains belonged to Liu, but police still do not know how she died.
Investigators are also still zeroing in on the location of the murder.
Police wouldn't provide further details on Wednesday on the torso that was found, but asked the public for help identifying the remains.
"We're in the early stages of our investigation so we're appealing to the public," Dunkley said.
"It's a very serious case, a very serious incident, and we're going to do our best to get to the bottom of it."