Ontario Premier Kathleen Wynne is splitting her finance department in half, appointing a powerful minister whose sole job is to wrestle down the massive deficit and deal with record-high debt.

In her first major act since winning a majority government earlier this month, Ms. Wynne is looking to signal that she is serious about dealing with the province's ballooning fiscal woes. She will vastly expand the post of Treasury Board president to include oversight of Crown agencies and responsibility for tough negotiations with government unions, Liberal sources said.

The Premier will put her closest political ally, Deputy Premier Deb Matthews, in the post – part of a sweeping cabinet shuffle to be unveiled Tuesday.

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Ms. Wynne won election on a left-tilting platform, including the creation of a new provincial pension plan and the promise of $29-billion in spending on transit and other infrastructure. But the Liberals' fiscal planning also calls for the $12.5-billion deficit to be eliminated in three years, with ambitious targets to restrain program spending and labour costs.

The province's credit was downgraded two years ago and some feared it could take another hit this year with the big-spending budget, which will be reintroduced next month. The expanded Treasury Board role appears designed to head off the possibility.

Previously, the Treasury Board presidency was a minor job, usually performed by the finance minister, which consisted of approving day-to-day spending and ensuring it was in line with the budget. Finance Minister Charles Sousa will remain in charge of broad economic policy and budgeting, while handing off many of his other duties to Ms. Matthews.

The cabinet shuffle will include several other major changes, insiders said. Eric Hoskins is expected to replace Ms. Matthews as health minister, a post she held for nearly five years. Brad Duguid will be promoted to Mr. Hoskins's old job at economic development, but will add responsibility for infrastructure and employment to the role, making him one of Ms. Wynne's most important ministers. Backbencher Steven Del Duca will join cabinet as transportation minister, replacing Glen Murray, who will move to environment. Reza Moridi will become training, colleges and universities minister on top of his current duties at research and innovation.

Some heavyweights, including Education Minister Liz Sandals, Attorney-General Madeleine Meilleur, Energy Minister Bob Chiarelli and Community Safety Minister Yasir Naqvi, will remain in their current roles. Mr. Naqvi will also take on the job of government house leader, left vacant with the retirement of John Milloy.

At Treasury Board, Ms. Matthews's toughest task may be facing down the government unions. The Liberals' budget contains no new money for wage increases, which could set up rounds of fractious negotiations. Ms. Wynne has vowed not to impose contracts through legislation, meaning Ms. Matthews will have to persuade workers across government to do without raises or find the money from savings elsewhere.

Negotiations with the teacher unions, whose contracts expire this year, proved politically damaging to the Liberals during the last round of talks, when then-premier Dalton McGuinty imposed a wage freeze. The teachers turned on him, campaigning against the Liberals. Ms. Matthews will have a hand on this file from Ms. Sandals, who helped defuse the tension between the unions and the government after Mr. McGuinty stepped down.

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Complicating labour relations further, several major unions – including the nurses and provincial police – ran attack ads against the Progressive Conservatives during the election, and may feel they helped the Liberals win the vote.

Overseeing Crown corporations will also be tough: the Ontario Lottery and Gaming Corporation is in the middle of a modernization process aimed at returning more revenue to the government.

Ms. Matthews is generally seen as one of the government's steadiest performers, bringing down the rate of budget increases in health and dealing with the fallout of the scandal over the ORNGE air-ambulance service.

Mr. Hoskins, a medical doctor best known for his humanitarian work in war zones, ran for the party leadership last year, losing to Ms. Wynne. He will have plenty of help at health, including recently appointed deputy minister Bob Bell, a well-respected former head of Toronto's University Health Network of hospitals. Also assisting Mr. Hoskins will be Dipika Damerla, who will take the newly created job of associate minister for long-term care.

Backbencher Mitzie Hunter will also receive an associate minister job, specifically tasked with helping Mr. Sousa implement the pension plan.

Mr. Del Duca, who has represented the Toronto-area riding of Vaughan since 2012, is one of the Liberals' most partisan members. Known for playing the role of attack dog in the last parliament, he had to apologize during the election after his campaign literature contained a photo that inserted Progressive Conservative Leader Tim Hudak into a scene of an exploding hospital from the film The Dark Knight. But he is generally viewed as a strong communicator and a good organizer, who will now be in charge of one of Ms. Wynne's priority files.

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The only other backbencher to receive a full ministerial job will be Helena Jaczek, who will take on community and social services. An MPP since 2007, she most recently served as chair of caucus and parliamentary secretary to Ms. Matthews.

No one currently in cabinet will be relegated to the backbench, a source said.

Former environment minister Jim Bradley who, at 37 years , is the longest-serving member of the legislature, will remain in cabinet as a minister without portfolio.