TORONTO, Nov 28 (Reuters) - Locomotive engineers at Canada's largest railway walked off the job on Saturday after talks broke down, but Canadian National Railway (CNR.TO) (CNI.N) said it was using management and non-union staff to provide "the best possible service under the circumstances."

CN spokesman Mark Hallman said the strike started overnight after the breakdown of talks with the Teamsters Union. "We have deployed our contingency plan," he said.

Dan Shewchuk from the Teamsters Union could not say how long the strike might last.

The union also said said commuter train services in the Montreal area would not be affected.

The engineers have been without a contract since Dec. 31, 2008, and CN unilaterally imposed new work conditions on Monday, describing this as the only way to break a deadlock.

Hallman declined to say how many trains were running, or indicate the possible impact the strike might have on CN results. Canada's rail network is heavily used by grain shippers and other exporters of raw materials.