The National Energy Board said the company now wants to route a 4-km (2.5-mile) portion of the project through Burnaby Mountain, a conservation area in Metro Vancouver.

"In order for the board to properly assess this pipeline corridor, we require more information and study," Sarah Kiley, a spokeswoman with the NEB, told reporters on a conference call.

Kiley added that the company would have until Dec. 1 to complete the required studies and submit them to NEB for review.

The NEB now expects to release its final recommendation on the proposed expansion by Jan. 25, 2016, rather than a previous deadline of July 2, 2015. The federal government will then have 180 days to review the recommendation and make its final ruling.

The C$5.4 billion ($5.02 billion) twinning of the pipeline, which carries crude from the Alberta oil sands to British Columbia's Pacific Coast, would boost capacity to 890,000 barrels per day from its current 300,000 bpd.

The project is facing increased opposition from local municipalities and environmental groups, who say they are unhappy with the answers they are getting from the Texas-based company on safety, costs and other issues during the review process.

($1 = 1.0753 Canadian Dollars)

(Reporting by Julie Gordon; Editing by Mohammad Zargham)