OTTAWA -- Stephen Harper's rivals defended the costs of their campaign promises Wednesday and the Conservatives deflected bad news from international analysts in a spurt of last-minute positioning before a leaders debate on the economy.

Harper has been thumping his chest since Finance Department figures released Monday showed that the federal government booked a $1.9-billion surplus for 2014-15 -- a year earlier than projected. The Conservatives have not released a costing of their platform promises.

But on Wednesday, 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.

The international organization blamed lower prices of natural resources for the slip in projected growth in countries that depend on such exports, such as Canada and Australia. It also downgraded 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.

"We are living in a very fragile global economy which is precisely why we need a serious, grown-up national government that is focused on job creation, fiscal discipline and lower taxes," said Conservative candidate Jason Kenney, speaking on behalf of Harper.

"We see those reports as underscoring our economic message."

Harper, NDP Leader Tom Mulcair and Liberal Leader Justin Trudeau all converged on Calgary, where the Globe and Mail-hosted debate is scheduled for Thursday evening.

Trudeau told reporters his promises are all costed within a fiscal framework the party released weeks ago. That framework includes a proposal to run deficits for the next three years, in order to pay for a $60 billion infrastructure spending plan, but is short on specifics about the costs of various smaller promises.

"The Liberal party was the first party to put out a complete fiscal framework and our opponents know that very well, they've been attacking us every single day," said Trudeau.

"All of our commitments, every commitment we make and every announcement across this campaign, is not only fully costed, but fits into that detailed framework that we announced weeks ago, before any other party did."

Mulcair's team was scheduled to release a full costing of his campaign promises on Wednesday afternoon. The NDP platform has been criticized by Trudeau in particular as unfeasible, since Mulcair has vowed not to run deficits, while paying for such items as a $15-a-day national daycare program.

But issues breaking outside of the economic ambit crept into the campaign dialogue.

A Federal Court of Appeal decision on Tuesday overruling the Conservative government's attempts to ban face coverings at citizenship ceremonies provided yet another opportunity for the parties to stake out their value positions.

Immigration Minister Chris Alexander announced the decision would be appealed to the Supreme Court of Canada. The government has 60 days to formally ask for leave to appeal.

"This is a secular ceremony," said Kenney, the longtime minister of multiculturalism, now defence minister.

"We find it completely inappropriate to hide one's identity."

Trudeau criticized the Conservative position.

"In Canada, we protect minority rights. That's one of the things that makes us an extraordinary country, strong not in spite of our differences, because of them," he said.

"In any situation where a government chooses to limit or restrict individual rights or freedoms, it has to clearly explain why. This government has not done that, it is continuing with the politics of division and even fear, and that is not worthy of a country as diverse and extraordinary as Canada."

Both Trudeau and Mulcair were meeting Wednesday with Calgary Mayor Naheed Nenshi, a figure who carries symbolic weight for both federal parties. Nenshi's centrist, socially liberal municipal leadership runs against type for conservative Alberta.

The Liberals and NDP see his success and that of Premier Rachel Notley as inspirational.