Paris's Charles de Gaulle (Roissy) and Orly airports are the closest intercontinental links with the region. Direct trains connect Paris to all main cities in Normandy. From the St Lazare train station you have connections to Rouen, Le Havre, Caen, Deauville and Cherbourg. And from the Montpamasse train station to will have trains to Alençon and to Mont Saint Michel.
Traveling by car you will have to take the A13 from Paris to Rouen (1.5 hrs). From Rouen you then take smaller roads to Caen and Le Havre.