Agency spokeswoman Roxanne Daoust says three investigators are assessing the derailment to determine what kind of investigation is needed.
CN says there were no injuries when 35 cars and one locomotive went off the rails near Edmundston, N.B., on Friday afternoon.
In a statement issued Saturday, the company says crews are removing the derailed cars and repairing the track.
Jacques Doiron, the Emergency Measures co-ordinator for Edmundston, said most of the cars contained wood and paper products, but some of the derailed cars were empty crude oil tankers.
Doiron said there were no leaks and no need for an evacuation.