But it's still unclear exactly how much cash the sale will generate for the federal government.

Harper has repeatedly insisted the government will erase the deficit despite the oil slump — a promise that could be key to his chances in this year's election, scheduled for October.

The transaction came a few days into the 2015-16 fiscal year, which means the proceeds will help pad the bottom line in this year's budget. The budget will be delivered April 21.

In November, the government predicted a $1.6-billion surplus for 2015-16, but crude prices tumbled even further in the months that followed. The lower oil prices are expected to indirectly siphon billions of dollars from federal revenues.

The oil slump also forced Finance Minister Joe Oliver to take the rare step of postponing the release of the budget until April. The fiscal blueprint is usually presented in February.

Oliver said his department needed more time to get a handle on the market instability caused by the oil shock.

In hindsight, however, observers and political opponents wonder if postponing the budget until April was done — at least in part — to allow the government to put the proceeds from the stock sale on the books in the current fiscal year.

"The Conservatives would sell the gold out of their grandmothers' teeth right now," said Liberal finance critic Scott Brison, who also thinks the Tories delayed the budget to draw attention away from the high-profile criminal trial for suspended senator Mike Duffy.

"They will do anything to create a surplus on the eve of an election."

Brison said one-time asset sales only help create surplus in a single year.

NDP industry critic Peggy Nash said the timing of the GM sale seems suspect with the budget's release only a couple of weeks away.

The Conservatives, she added, are searching for ways to balance the books after introducing big-ticket tax breaks aimed at families.

In a letter to his caucus colleagues Tuesday, Oliver also hinted the government could make good in the budget on its 2011 election-campaign promise to double the contribution limit on tax-free savings accounts in the budget.

"It seems as though the Conservatives have made a decision to sell the shares simply because it's a politically convenient time," Nash said Tuesday.

"Whether Canadians are getting the best deal for their investment remains to be seen."

On Monday, Oliver said in a statement that the GM sale means taxpayers are no longer exposed to the market.

The government had long voiced its intention to sell the shares.

"We never believed the government should be a shareholder of a private sector company for an indefinite period of time," Oliver said.

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By Andy Blatchford, The Canadian Press