SHOULD HAVE KNOWN BETTER THAN TO SUCCUMB TO THE OIL CURSE:

Polls indicate that Harper's right-of-center Conservative party, which has been in office since 2006, could lose its majority in the House of Commons.

That would leave Harper at the mercy of the two main centre-left opposition parties, who could unite to bring him down. Minority governments in Canada rarely last more than 18 months.

Harper, 56, says only he can be trusted to manage an economy that is struggling to cope with the after-effects of below-par global growth and a plunge in the price of oil, a major Canadian export.

The Conservatives are trailing slightly behind the left-leaning New Democrats (NDP), who have never governed Canada. The Liberals of Justin Trudeau are well behind in third.

Both parties say Canada needs a change from Harper, who has cut taxes, increased military spending, toughened the country's criminal laws and streamlined regulations governing the energy industry.

Five of Canada's last six election campaigns have lasted the minimum length of just over five weeks.

The Conservatives have deep pockets and the campaign - the longest in modern Canadian history and the third longest on record - will allow them to run a wave of attack ads. 

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