Canada's federal government says it will buy an oil pipeline to the Pacific coast to ensure it gets built.

Prime Minister Justin Trudeau's government plans to spend $4.5 billion Canadian (US$3.4 billion) to buy the controversial Trans Mountain pipeline.

Kinder Morgan halted essential spending on the project and said it would cancel it altogether if the national and provincial governments could not guarantee it.

Finance Minister Bill Morneau said Tuesday the pipeline must and will be built.

The line would allow Canada to diversify and increase exports to Asia, where it could command a higher price. But there is stiff environmental opposition.

Canada has the world's third-largest oil reserves but 99 percent of its exports now go to refiners in the U.S., where Canadian oil sells at a discount.