OTTAWA - Stephen Harper planned to use a speech Friday afternoon to a large Muslim gathering to trumpet a new economic report that he says validates his government's policies.

The Conservative leader did not do any formal campaigning, instead choosing to address the Ahmadiyya Muslim Jama'at, Canada's largest national Islamic convention, which kicked off a three-day conference in Mississauga. Harper planned to use the event to highlight what he saw as good news in the Department of Finance's monthly Fiscal Monitor.

It reported a $5-billion surplus for the April-to-June period this year. However, it attributed almost 40 per cent of the gain to the government's one-time sale of General Motors shares in April.

Harper issued a written statement shortly after the monitor was released, saying it meant that his Conservative government was "ahead of the game" on its budget plan.

The Liberal campaign accused Harper of not telling the truth, saying he is actually running a deficit, despite his claims to the contrary.

Harper spent part of Friday in Toronto shooting new television commercials.

NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau were both in Montreal, still arguing over which party has the best economic plan for the country.

Trudeau was joined by former prime minister and finance minister Paul Martin for the second time this week and the elder Liberal statesman stole the spotlight. Martin, who balanced the country's books in the 1990s as the Liberal finance minister, called Harper "the king of deficits."

Martin delivered a fiery speech aimed at buttressing Trudeau, who staked out fresh ground this week by saying he would run modest deficits to 2019 in order to pay for new infrastructure investments that he said are essential to spurring long-term economic growth.

The NDP and Conservatives have promised balanced budgets, prompting Martin to say: "That Tom Mulcair is now a student of Stephen Harper's economy makes absolutely no sense."

Mulcair, himself a former Quebec cabinet minister, fired back at the Liberals, calling Martin, "the king of austerity."

Mulcair accused Martin of trimming social and health transfers to the provinces by almost one-quarter, while cutting employment insurance and housing spending.

"Could you be a little more discrete before you criticize the NDP's balanced, realistic approach to taking care of future generations?" Mulcair asked.

While this week marked a sharp shift in the federal campaign toward economic issues, the Mike Duffy trial, which knocked the Conservatives off message repeatedly during the early days of the campaign, again reared its head.

A CTV reporter, Robert Fife, doggedly pursued Ray Novak, Harper's chief of staff, through the streets of Ottawa's Byward Market on Friday morning, with a camera recording it all.

Last week, Benjamin Perrin, formerly a lawyer in Harper's office, testified that Novak was present when Nigel Wright, Harper's former chief of staff, said he was going to cover Duffy's $90,000 in dubious expense claims with a personal cheque.

Novak initially refused to discuss the matter and was repeatedly questioned by the reporter. He eventually said: "I did not know that Mr. Wright was going to cut that cheque."

Novak also said he didn't see an email from Wright informing him about the payment until "it was disclosed much, much later."

Mulcair said he was less interested in subordinates of the prime minister, as he once again urged Harper to "come clean to Canadians" and "start telling the truth" about the Duffy matter.

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The Liberal campaign responded with a statement that posed a series of questions to Harper and urged him to "finally end the coverup and come clean with Canadians."

Harper has steadfastly refused to comment on evidence coming from the courtroom, saying it is an ongoing legal proceeding.

He has consistently said only two people are responsible for any wrongdoing in the affair: Duffy and Wright.