If you are heading upto Calais from DLRP, the best thing is to take a train from Marne-la-Vallée to Lille Europe, and from there to Calais. The total travelling time is about 2 1/2 hours, including the change at Lille Europe. It's pretty quick, very efficient and there are loads of trains every day. For exact prices and times, check http://www.sncf.com/indexe.htm which will allow you to plan your journey.
Of course if you are visiting from the UK, make sure to bring lots of Cadbury's chocolate...the easy way to keep CMs like me happy!
Thanks so much Disneyfan@Paris. I will check out the site you gave. We are from Glasgow but now live in Canada. We hope to see Paris, London and Glasgow on our next trip.
Thanks again