The group, which includes housebuilder Stewart Milne and shipping businessman Douglas Craig, aims to raise £15m of private-sector money for the capital costs in addition to a potential further £15m in endowments ahead of the vote by Aberdeen City Council.
The scheme is already backed by £50m from oil tycoon Sir Ian Wood, who will also cover up to £35m of any overspends.
Supporters yesterday claimed any other councillor in any other local authority in the country would give their right hand for a business community willing to stump up so much money.
They warned that when everything was included the city would lose £182m of investment in the regeneration of its centre if the council was to vote against the City Garden Project.
Sir Ian and others have also tied the project into Aberdeen's attempts to become European City of Culture in 2017, citing Creative Scotland's claim that it would not be a serious contender without it.
However, opponents say the European bid could still succeed if the project is not approved. They hope to address councillors on the plans of the previous administration to use Tax Incremental Financing (TIF) to secure £92m for the project to carry out additional redevelopment around the gardens.
They see the report supporting the TIF bid as deeply flawed, and claim there is a £35m funding gap.
Mr Craig, chairman and managing director of shipping and energy services firm the Craig Group, said: "As a businessman who has grown up, studied and prospered here in Aberdeen, I have a responsibility for the next generation and the generation after that to help secure the best possible future for them.
"I am totally behind the City Garden Project and, if it goes ahead, will be making a substantial financial contribution as well as actively fundraising to reach the overall target."
Mr Milne, who is also the chairman of Aberdeen FC, is confident the private donations will be secured if the project gets the green light tomorrow. He said: "There has been much talk and concern about securing the outstanding £15m from private investors. Speaking to other businesses in and around Aberdeen I am confident this will not be an issue, but naturally there is a reluctance to come out and support a project which is hanging in the balance. Should the initiative go ahead then that is the time that names and pledges will come forward."
However, Mike Shepherd, chairman of the Friends of Union Terrace Gardens who have campaigned against the plan, said if it was an ordinary householder facing the decision, it would be clear what to do: "The builders are in town, money's too tight to mention and you haven't been given a reliable estimate for that extension you like the look of. What's the advice? Walk away or you will lose your shirt."