I spent a couple of weeks in the maritimes in 2003 for my honeymoon. Wouldn't trade it for the world. I'm actually itching to go back.
We spent a couple of days in Halifax which is a great city. We did the usual stuff like the Citadel, wondering around the city, going to a few pubs, etc.
We then drove south and took in some of the smaller towns along the way. Peggy's Cove was nice, of course, but there are a lot of cool things all the way around the coast. One highlight was a drive along "Digby Neck" on the Fundy coast. You need to take a couple of ferries to get all the way to the end, but there are some nice views and a couple of quaint little towns.
One thing about driving around Nova Scotia - there's often a choice for the coastal road or the inland road. Definitely take the coastal road. The main highways are obviously faster as they don't wind around the coast, but all you'll see are trees, trees, and more trees. I was actually surprised at how many trees there are in Nova Scotia. So if you're planning out a drive, make sure you estimate your times based on the scenic routes because that's where you'll find the towns and villages that the East coast is famous for.
PEI was amazing. Cavendish beach ranks up there with one of the neatest I have ever been on. Lots of sand. There's a bunch of tacky touristy things nearby that you'd probably be better off avoiding (Anne of Green Gables stuff, Ripleys Believe it or Not, etc.) but as soon as you get onto the beach, the not-so-savoury tourist stuff is all forgotten.
There are also a load of little country roads on PEI that will get you pretty much anywhere you want to go. We had a great time criss-crossing the island on these little roads. It reminded me a lot of England, actually.
New Brunswick got the short end of the stick as we didn't have time to see more of it, except for the part leading to the bridge to PEI. We actually diverted to Moncton because my wife wanted to see magnetic hill. Not worth the diversion, but I'm sure that Moncton has a lot more to offer that we didn't have time for.
Cape Breton is another area that we didn't have time for, but on our next trip we're going to have to do it.
The final stop on our trip was a jaunt to Newfoundland. Highly recommended. I enjoyed the entire vacation, but the part that stands out the most for me is Newfoundland. I found the rest of the trip to be different and interesting but still quite Canadian. Newfoundland felt the least like Canada - and I mean that in the best possible way. The accents, the buildings in St. John's, the terrain, etc. It honestly felt like we were in another country. If you're using your air miles, I'd definitely recommend a quick trip to Newfoundland if you've never been.
Dammit - now I need to go back.