CALGARY -- Expect to see a fired-up Stephen Harper bounding out of his corner and spoiling for a fight with NDP leader Tom Mulcair in tonight's main event on the economy.

Harper has been the recipient of some rare good news this past week in what has so far been a less-than-stellar campaign for the Conservatives, attacking on the economic flank and basking in the glow of Monday's budget news.

Economic data released at the start of the week showed the Conservative government actually posted a $1.9-billion surplus in 2014-15, despite projections of a deficit -- balancing the books a year earlier than expected.

The Finance Department released the year-end fiscal figures Monday for a period the government had predicted to instead generate a $2-billion shortfall. It ended a streak of six straight deficits under the Harper government.

That news was tempered somewhat after the Organization for Economic Co-operation and Development lowered its estimate for Canada's economic growth this year to 1.1 per cent -- down 0.4 of a percentage point -- as well as its projections for growth in Canada in 2016.

Moody's Investors Service also cut its outlook for Canadian Oil Sands Ltd, due to falling oil prices.

"What we know about Harper it's going to be an attack and certainly in this debate he's going to go negative -- he has to drill into the New Democrats and show again that Trudeau isn't ready," said David Taras, a political science professor at Calgary's Mount Royal University.

"I think what they're going to do is try and hone the ballot question, which is, "It's either us or it's chaos."

Despite a surge in Justin Trudeau's popularity numbers, the Conservative campaign continues to dismiss him as a real threat -- often ridiculing him at campaign events for his infamous "the budget will balance itself" remark and his plan to run deficits to finance his infrastructure spending initiatives.

It is Mulcair that is most vulnerable to Harper's attack, said Taras, who expects the Conservative leader to push himself as the best possible caretaker of the Canadian economy.

"I think (Mulcair) is trapped by the fact he says there's not going to be deficits, but he's made substantial promises on daycare, infrastructure and more police on the streets ... and for a lot of Canadians the math does not add up," said Taras.

"Mulcair has to square that circle and certainly Harper is just going to go after him hammer and tongs on the economy, as will Trudeau."

The chance of an overwhelming victory or proverbial "knockout punch" in any debate is rare, he added -- debates typically just reinforce pre-existing impressions, unless someone really does stand out or land a rhetorical roundhouse.

But Taras said he's skeptical about the prospects of the Conservatives turning things around with tonight's debate.

Harper, he said, is still "a man under attack" and two out of three Canadians don't want to vote for him.

"This is an uphill battle," Taras said. "We may be watching the prime minister sink into a political oblivion from which he can't get out."