Canada's prime minister, Stephen Harper, is expected to try to suspend the parliament in an unprecedented move to delay a confidence vote next week that could topple his government.

As Canada headed into uncharted constitutional waters, Harper was due to address Canadians on the political crisis in a televised speech as he moves to head off a confidence motion tabled for Monday.

He is expected to ask the country's governor general, Michaëlle Jean, to suspend parliament until next month after the Liberals, New Democrats and Bloc Québécois, which together control a majority of the 308 seats, signed a pact last Monday agreeing to vote to oust his minority government and pave the way for their own proposed coalition.

Harper has said all legal means are being pursued to stop the opposition's plans.

Jean, who represents the Queen, holds a mostly ceremonial position but it will be her decision on what to do. She is expected back in Canada after cutting short a European trip. The crisis could force the second general election in two months, lead to an opposition coalition taking power, or a suspension of parliament until January.

A governor general has never been asked to suspend parliament to delay such a vote when it was clear the government no longer had the confidence of a majority of legislators.

"We are in uncharted territory," said Ned Franks, a constitutional scholar at Queen's University in Kingston, Ontario.