Statements from both sides said there were high level discussions on Sunday and the two sides agreed to continue talking.
CN says it hopes to reach a negotiated settlement or to persuade the union to agree to binding arbitration.
The railway said Friday that it intends to lock out the 4,800 workers represented by Unifor at 11 p.m. Monday unless the union agrees to binding arbitration to settle contract differences.
The union, which has announced plans to begin a strike vote next week after the failure of five months of negotiations, rejected the company ultimatum.
A union statement says there was "meaningful dialogue" on Sunday between Unifor National President Jerry Dias and CN President Claude Mongeau.
Last week the Teamsters reached an agreement with Canadian Pacific Railway after a one-day strike. That deal made a number of improvements, including rail safety and working conditions.
The agreement came after the federal government moved to bring in legislation to end the strike.
A statement from federal Labour Minister Kellie Leitch made no hint of such a move in the CN talks. It only said Leitch has been in touch with both sides and welcomed the resumption of negotiations.
She said both sides have promised that commuter rail service in Montreal will not be affected by any work-stoppage.