Emergency responders descended on the home and the "hazardous" chemicals were found in the yard of the upscale home, which belonged to Byron Sonne whose trial wrapped up on Monday.
Police would only say they went to the house and found materials they considered dangerous in the backyard.
However, a source said the discovery was a direct result of the trial.
"Something apparently came up (in court) in which the issue arose about whether there were any dangerous substances in his location," the source told The Canadian Press.
Another source said the chemical was potassium chlorate for rocket fuel which Sonne made reference to in an Internet chat he had before his arrest in June 2010.
During the chat, Sonne commented about a "storage magazine buried in a shady spot in the backyard" because he did not want that much of the hazardous substance inside the home.
The Crown and the officer in charge of prosecuting Sonne had access to the information, raising questions about why they didn't raise the matter while the case was ongoing if they considered it of importance.
It was not immediately clear whether the prosecution would now seek to re-open the case in light of Wednesday's find.
Several homes were evacuated and officers asked other nearby residents to stay indoors and away from windows as the chemical, a powerful oxidizer, was removed.
Const. Wendy Drummond said the contents of a container caused "concern" for experts and posed a threat to the public.
"We have located ... a container and in that container are additional sealed containers with what we believe to be some type of explosive dangerous material or substance," Drummond said.
The materials were taken to a location on the Toronto waterfront where they would be destroyed on Thursday, she said.
Sonne, 39, is charged with four counts of possessing explosives and one of counselling mischief not committed.
Closing submissions ended Monday, and Ontario Superior Court Justice Nancy Spies reserved her decision, which she is to render this month.
During those submissions, Spies asked pointed questions of the prosecution, even suggesting at one point there could be a "fatal flaw" in its case regarding one of the explosives counts.
Because Sonne's charges are still before the courts, his lawyers refused to comment on Wednesday's development.
Police initially arrested Sonne and raided his home in the days leading up to the tumultuous summit.
Among other things found in the home were laboratory apparatus and numerous chemicals, which the prosecution alleges Sonne intended to combine into explosives.
No actual explosives were found.
Sonne, a self-described security and computer geek, maintains he was trying to expose flaws in the G20 security, and that he had no plans to make bombs out of any of the legal chemicals he had.
He said he had the substances — including potassium chlorate found at the time in the house — for his rocketry hobby and to make crystals.
Sonne himself could not be reached immediately, but his mother Valerie Sonne, who along with her husband had been following the trial closely, said the family was unable to talk about on the police find.