Former Ontario deputy premier George Smitherman is endorsing Olivia Chow in Toronto's mayoral race, joining an expanding group of prominent movers and shakers quietly lining up behind the New Democrat MP.

Sources close to Ms. Chow say supporters are laying extensive groundwork for a possible campaign, even though Ms. Chow says she has not made up her mind about challenging scandal-plagued Mayor Rob Ford in next October's vote. They are building up communications, fundraising and outreach infrastructure, and securing the backing of numerous key people.

Besides Mr. Smitherman – a Liberal who lost the 2010 mayor's race to Mr. Ford – other figures who have pledged their support for Ms. Chow include filmmaker Deepa Mehta, former Royal Bank executive Charles Coffey, former provincial cabinet minister and United Way CEO Frances Lankin and Dr. Joseph Wong, a leader in Toronto's Chinese community. Some veteran municipal politics strategists say that all of Mr. Ford's opponents, left, centre and right, should unite behind one candidate in the coming election, to guard against splitting the vote.

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Mr. Smitherman told The Globe and Mail he visited Ms. Chow at her Chinatown home roughly six weeks ago to encourage her to run and offer his "unwavering support" if she does. Ms. Chow, he said, would bring stability back to the city after the drug, drink and gang allegations surrounding Mr. Ford. Central to her campaign will be her personal story – she immigrated from Hong Kong in her teens – and the suggestion that her humble origins will make her a careful manager of Toronto's finances, sources said.

"I like her values, I've known her to be a progressive pragmatic and I especially like her maturity," Mr. Smitherman said. "At this stage in our city's life, with all of what's been going on at city hall, drawing somebody who knows city hall but has not been part of this charade would be a good re-start point."

It will surprise many that Mr. Smitherman, who was widely seen as the candidate of the centre in the last election, would back a staunch leftist. But he compares Ms. Chow to his own political mentor, former mayor Barbara Hall, whom he credits with building the city's economy by kick-starting development of the waterfront.

"She was a lefty who actually accomplished a lot," he said. "I see a lot of similarities between her and Olivia."

Mr. Smitherman said he is willing to help in any capacity Ms. Chow requires and has already been passing on "intel" to her campaign team – what he learned after seeing his massive lead in early opinion polls evaporate as Mr. Ford romped to office. He told her, he said, that there is no need to sign up early.

Mr. Ford, TTC Chair Karen Stintz and former city budget chief David Soknacki have already announced their intention to run. Radio host John Tory, a former provincial Progressive Conservative Leader who lost the 2003 mayoral race to David Miller is also mulling a bid, as is Councillor Denzil Minnan-Wong, a former Ford ally who defected after Mr. Ford admitted to having smoked crack cocaine.

Organizing for Ms. Chow has been under way roughly a year. The people at the heart of the campaign team are Joe Cressy, an NDP organizer who ran Ms. Chow's federal re-election bid in 2011, and John Laschinger, one of the city's most seasoned campaign managers, who helped put David Miller and June Rowlands in the mayor's office.

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One source said Mr. Cressy initially approached Mr. Laschinger around the time Mr. Ford looked set to be kicked out of office over a conflict-of-interest conviction late last year. Mr. Laschinger met with Ms. Chow over coffee, then began to prepare for the possibility of an early mayoral election in January of this year. In short order, the team had lined up an advertising firm, fundraisers, plus a group of advisers and organizers, the source said. An organizational chart had been drawn up in pen and pencil.

When a higher court overturned Mr. Ford's conviction, Mr. Cressy and Mr. Laschinger settled in for the longer task of building a team for the vote in October, 2014.

In an e-mail, Mr. Cressy lauded Ms. Chow. "I hope she decides to run for mayor as she could bring dignity and pride back to our city," he said. Mr. Laschinger declined to be interviewed, but expressed his support for Ms. Chow.

In an e-mail to the Globe, Ms. Chow said she is "seriously considering running for mayor," but had not made a decision.

"Over the last few months I have heard from many people from all corners of our city and beyond who are encouraging me to run for mayor," she said. "And whether it is people coming up to me on the street or at community events, what I frequently hear is just how proud people are of Toronto and what can be achieved."

Two sources suggested that, if Ms. Chow runs, she would not enter the race until at least February. Her memoirs are due out next month, after which she will be on tour promoting them. One source said declaring later would also allow her to enter after the annual budget comes out.

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If she does, she will have a broad support base to build on.

Ms. Mehta, the director of Midnight's Children and Oscar-nominated Water, helped fundraise for former Liberal premier Dalton McGuinty during the 2011 provincial election. "Now more than ever we need a Mayor who cares and unites across the board. Olivia Chow unites," Ms. Mehta said in a statement provided to people close to Ms. Chow.

Mr. Coffey is a lifelong Grit who once ran RBC's government relations department and has many friends in high places. He worked with Ms. Chow a decade ago when she was a city councillor and Toronto's children's advocate, and he co-chaired a commission on early learning and child care with philanthropist Margaret McCain.

Mr. Coffey said he encouraged Ms. Chow to run over breakfast at the Epic Restaurant in the Royal York Hotel last spring. If she enters the race, he said, he is prepared to host an event at his North York home to introduce her to his many connections, and raise money for the campaign. He said he was drawn to Ms. Chow by her "social justice mindset."

"I have often described her as a consensus builder," he said. "She has, in my view, this unique ability to reach across, whether it be party lines from a political perspective or different points of view, to bring people together."

Ms. Lankin held the health and economic development portfolios in the NDP government of former premier Bob Rae. Later, she spent a decade running the Toronto chapter of the United Way. Most recently, she co-chaired a government review of social assistance and served earlier this year on Premier Kathleen Wynne's transition team.

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"I am looking to support a true city builder who understands the need to provide supports and services to people in all Toronto neighbourhoods," she wrote in an email. "Today too many people are being left behind."

Dr. Wong, a family physician and philanthropist, founded the Chinese Canadian National Council and the Yee Hong Centre for Geriatric Care. He also started the annual Dragon Ball, which marks the Chinese New Year in Toronto, to raise money for Yee Hong. He confirmed in an e-mail to the Globe that he had encouraged Ms. Chow to run.

With reports from Jeff Gray and Elizabeth Church