Join Date: Jul 2010
Location: Montreal Canada
The Confederation Trail is gravel, but a good surface that is like rail trails around here that have been converted to bike trails, from what I have read, the surface there is like the ones here, very rideable on 25-28 slicks. I'm sure you can get more specific info from some east coast forums about various sections of the trail.
All that said, PEI has some of the most polite, cautious car drivers you will ever see (without being mean, many of them drive so slow it can be frustrating sometimes in a car) and my recollections of driving there on a family vacation a bunch of years ago are that riding on the main highway would not be a problem in terms of traffic and drivers being respectful of bicycles.
You should be able to find good info on riding the Cabot Trail, and as in all coastal areas, be prepared for windy conditions sometimes. Bike touring info should give you an idea of predominant wind directions that are usually good to be aware of for planning a route.
ps, I was at a bike show last weekend and spoke with reps from an event in PEI, a supported 3 day ride named Granfrondo PEI, look it up if this sort of thing appeals. Its in July I believe.