Canadian police are investigating the mysterious deaths of billionaire Barry Sherman and his wife Honey, whose bodies were found in their Toronto mansion yesterday.

Authorities were conducting post-mortem examinations today and treating the deaths as suspicious. A Toronto Police spokesman said that nothing had been ruled out in the probe.

Two Canadian newspapers reported that police were investigating the deaths as a possible murder-suicide, citing unidentified police sources.

Toronto Police Constable David Hopkinson said police are awaiting post-mortem results and no determinations have been made as to the cause and manner of deaths.

"There's a whole bunch of different scenarios here. We are not ruling anything out," he said.

He declined to say how or where the bodies were found in the home.

The couple's neighbours, business associates and some of Canada's most powerful politicians said they were saddened by the deaths.

"Our condolences to their family & friends, and to everyone touched by their vision & spirit," Canadian Prime Minister Justin Trudeau wrote on Twitter.

Toronto Mayor John Tory said in statement he was "shocked and heartbroken" to learn of the deaths, noting that the couple had made extensive contributions to the city.

"Toronto Police are investigating, and I hope that investigation will be able to provide answers for all of us who are mourning this tremendous loss," Mr Tory said.

The Shermans recently listed their home for sale for nearly C$7 million.

An estate agent discovered the bodies in the basement while preparing for an open house, the Toronto Globe and Mail reported, citing a relative.

Mr Sherman, 75, founded pharmaceutical firm Apotex in 1974, growing it by introducing large numbers of low-cost generic drugs that took market share from branded pharmaceuticals.

He stepped down as chief executive in 2012 but remained executive chairman.

Forbes has estimated Mr Sherman's fortune at C$3.2bn.

Apotex is the world's seventh-largest generic drug maker with 11,000 employees and annual sales of more than C$2bn in more than 45 countries, according to its website.

The couple was known for their philanthropy, giving tens of millions of dollars to hospitals, universities and various organisations, CBC reported.

"They were extremely successful in business, but also very, very giving people," former Ontario Premier Bob Rae told CBC. "It's going to be a very, very big loss."