In a release, Via says its train service has resumed between Toronto and Ottawa, as well as between Toronto and Montreal, in both directions.
Via says delays are expected throughout the day due to speed restrictions on the site and possible railway congestion.
The company said service between Montreal and Ottawa was not affected.
A spokesman for CN said seven cars of a westbound train derailed Saturday afternoon, but Brent Kossey said no injuries were reported and no dangerous goods were involved.
The cause of the derailment is under investigation.