I visited the First War battlefields several times from the UK. I always took the train from London straight to a central location, like Ypres, then hooked up with various tour companies that ran visits to the battlefields. There are also taxis and private citizens that will show you around. I did a ton of hitchhiking, but I'm cheap. When they find out you're Canadian they generally can't do enough for you - it's kind of embarrassing actually. Search the web for info like this before you go: http://www.1914-1918.net/tourist_ypres.htm
WW1 and 2 are big tourism business there, so don't feel like you have to rent a car if you don't want to. You can rent a bike, take a bus etc etc. I know we North Americans feel naked without a car, but you really don't need one. There are also ample guide books in just about every major centre, so plan on making some plans while you're there based on the info you dig up locally and just wander around. I literally stumbled on some very intersting sites out of the blue "I slept on Hill 60" (but be careful about the 'iron harvest' - piles of UXBs!). The Normandy area is called 'The Invasion Coast' and there are a series of guidebooks that cover just about every battlefield.
Must visits:
Tyne Cot Cemetery (Passchendale)
Ypres, Menin Gate, at 4.00pm for the Last Post
Vimy Ridge
Pegasus Bridge
Omaha Beach cemetery (as seen in Saving Private Ryan) and Pointe du Hoc
Mulberry harbour at Arromanches http://en.wikipedia.org/wiki/Mulberry_Harbour
Mont Ormel 'A Polish Hill' at Falaise http://en.wikipedia.org/wiki/Falaise_gap
Bény-sur-Mer Canadian War Cemetery http://en.wikipedia.org/wiki/B%C3%A9ny-sur-Mer_Canadian_War_Cemetery
Verdun is also amazing/ hideous, but it's quite a bit further away, on the French-German border.
You should read 'Back to the Front' if you can find it. This is a good book about visiting the WW1 battlefields, written by a Canadian living in the UK. Follow along with some of his writing. http://www.daedalusbooks.com/Products/Detail.asp?Media=Book&ProductID=57550&SubCategoryID=2153
Take good rain gear, fleece jacket and walking shoes/ boots as the weather can be grim. Enjoy yourself: quaff Belgian beer - the best in the world, bring back lace and chocolate, drink Calvados, takes millions of pictures (post some here when you get back), marvel at the achievements of our veterans. It's a unique, and very humbling, experience.