Ontario faces slower economic growth over the next 20 years, requiring more infrastructure spending and a stronger social safety net to counter the ill effects of that sluggishness, Finance Minister Charles Sousa says.

Mr. Sousa's Long-Term Report on the Economy, released Wednesday, projects average annual real domestic product growth of 2.1 per cent between now and 2035, an improvement from the province's post-recession lows but down from the 2.6 per cent average Ontario has enjoyed since 1982.

"It is actually less than anticipated, and that's a result of global forces around the world," he told reporters at Queen's Park. "It requires us to have even greater resolve in the province of Ontario to show some of that leadership, to show some of those strategic investments necessary."

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The document, released roughly a month before Mr. Sousa's budget, appears designed to pave the way for the spending plan, which is expected to include such infrastructure projects as a new highway between Kitchener and Guelph, a road in the Ring of Fire mineral deposit in the north and a light-rail line in Hamilton, along with more than a billion in new social spending. The budget will also create a new Ontario retirement savings system to supplement the Canada Pension Plan and a $2.5-billion fund to lure new businesses to the province.

The details of the budget were leaked to the Progressive Conservative Opposition, which then made them public Tuesday in an effort to spoil the government's public-relations plan for rolling out the budget. The Tories said they obtained the details from disgruntled bureaucrats.

The long-term forecast also appears to buttress Mr. Sousa's argument he can balance the province's books by 2017-18 by relying in part on economic growth. The GDP is projected to grow by 2.5 per cent annually until 2017 before slowing again.

Mr. Sousa, however, denied that the document was political. He said it merely shows that, with an aging population and a tough economy, the government must take action to create jobs and pump up the social safety net.

"My concern is ensuring that we provide and present and deliver a budget that is meaningful to the people of Ontario," he said.

PC finance critic Vic Fedeli said the long-term forecast was purely political, pointing out that the government didn't release it as scheduled in the fall but instead waited until shortly before the budget.

"Those numbers were to be turned over to the citizens of Ontario over six months ago," he said. "It's 100 per cent a political document."

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Mr. Sousa, meanwhile, said he was unconcerned over Wednesday's stunning budget leak, in which a rollout schedule that listed more than 20 different budget items to be unveiled over the next month was slipped to the PCs.

Asked if he was going to hunt down and punish the civil servant responsible for the leak, or call in the police, Mr. Sousa said: "I have great confidence and I respect the individuals who have been working hard in putting forward a document that is going to be extremely substantive and very visionary."