What is the best way to get from London to Rouen France on train? Chunnel to gare de norde and then is there a train to Rouen?
Yes. Trains to Rouen leave from Gare Saint-Lazare. You would have to taxi or metro between the two stations.
What you call chunnel is the Eurostar train (prices only rise after they are released for sale, they never drop), from London St Pancras International station and yes it goes into Gare du Nord. You then need a taxi or bus or RER to Gare St Lazare for the train to Rouen. That last train takes about 75 minutes.
Be sure to check in early enough for the Eurostar. All the border controls and security are dealt with before you board so you must not be late or you won't go.
You actually do not have to figure this out for yourself. Just go to "www.sncf-connect.com" and search for "London st. Pancras International" to "Rouen Rive Droite". Let the system work it out for you.
You will need to change stations, but the RER E goes direct form Nord to st. Lazaire, and being a new system has escalators and elevators etc... You can get your ticket for the RER on board the Eurostar.