Despite public support from a raft of current and former politicians Tuesday morning, Toronto Mayor John Tory says he's still not convinced the city would benefit from hosting World Expo 2025.

The mayor's comments came as his executive committee prepared to debate a city staff report that recommends the city not pursue a bid to host the international fair.

"There are so many unanswered questions at the moment that as a matter of honesty and responsibility I can't stand here and say I'm four-square in favour of this," Tory said.

Aside from the cost, Tory said he needs assurances that current infrastructure projects wouldn't be pushed aside in a city bid to host the fair.

Earlier Tuesday, Coun. Kristin Wong-Tam — who has been the proposed Expo's biggest supporter on council — held a news conference to introduce former mayors Art Eggleton and Barbara Hall, former premier David Peterson and the Liberal MP for Don Valley East, Yasmin Ratansi, all of whom voiced their support for an Expo 2025 bid.

Wong-Tam also quoted business and labour leaders who, she said, have agreed to cover the multi-million dollar cost of the bid.

Ex-mayors' support not swaying Tory

Asked if that support had softened his skepticism about the fair, Tory said: "No. I take note of the fact there are some people, community leaders and others, who are in favour and I certainly welcome that.

"I think people have an expectation of me that I would absolutely satisfy myself and them that this is a good investment of public money, and I would suggest it should not come from property taxpayers who are already hard-pressed and who have a list of other projects in front of them."

Prime Minister Justin Trudeau wrote a letter to Mayor Tory earlier in which he pledges his government will "explore next steps" if Toronto city council chooses to make a bid to host World Expo 2025.

Trudeau wrote the supportive comments in a letter addressed to Tory and his co-signatories, who had previously written to him about the potential bid.

"Should the city of Toronto choose to submit a bid to host an exposition ... our government is prepared to explore next steps," Trudeau wrote. "We are committed to strengthening Canada's place in the world as well as restoring our country's reputation as an active partner of the international community."

A copy of the letter was also sent to Canadian Heritage Minister Mélanie Joly and Foreign Affairs Minister Stéphane Dion.

'No taxpayer money is needed' for next step

World Expo is held every five years. It is a six-month long showcase of trade, innovation and products from around the world. The Expo was held in Milan last year and the next one will be hosted by Dubai in 2020.

​"By 2025, the entire planet will know we are here and that we aren't just ready to lead, but that we have been leading," Wong-Tam said outside city hall Monday morning.

She says private sector business leaders have agreed to foot the bill to create a business plan.

"A coalition of some 40 business leaders has written a letter to the mayor promising to raise the money to cover the costs of preparing a business plan. No taxpayer money is needed to take us to the next step," she said in a statement released Monday.

The councillor also said 25 leaders from across the labour, development, infrastructure and construction sectors have written a letter to city council in support of a bid.

"I think we have a responsibility now to respond to the prime minister," said Wong-Tam. "When he asks Toronto city council, 'Are you prepared to lead?' I would hate to think our answer is, 'No Mr. Prime Minister, we want you to tell the City of Toronto what to do.' That's not what I call effective leadership."

Mayor is cautious

On Monday Tory released a statement in which he said the city still does not know what financial contribution would be required on behalf of Toronto if the bid was successful and that the city would need to confirm that the federal and provincial governments would provide financial support.

The mayor also added that he would not want to see any funding that's already committed to transit, housing or other infrastructure locally be reduced or impacted should higher levels of the government agree to put money towards the Expo.

"My position is not meant to be negative. It's meant to be cautious and responsible," Tory said. "I appreciate the support we are seeing for an Expo bid this week but this doesn't reduce the need for a very honest, sensible discussion of the requirements set out above, among others, in making such an important decision."

Canada has only held the World Expo officially once before in Montreal in 1967. The event's regulatory committee classified Vancouver's Expo in 1986 as an "international specialized expo."

The official bid letter will have to be submitted by Nov. 1, 2016, according to Wong-Tam. Then the city has one year to develop a book and proposal with more details and plans which will be vetted and voted on in Paris. The host city will be announced in June 2017.