Can't help much with your timing I always found that the timing thingie was good to give you a rough idea. As for campgrounds I am more familiar with Nova Scotia , Pick up a Doers and Dreamers Guide from the Provincial Tourism Bureau Full of great ideas . On the campground side we always enjoyed the Provincial Parks , of which there are several along your route. On the
Peggy's Cove area , we enjoy Graves Island , has some beautiful large 2 way hooks ups although most of the provincial parks are site only. The Cape Breton Island area is a treasure full of good ideas.
Our only experience in PEI is Twins Shores campground , great spot and close to most of what you need. If I can be more specific ,send me a PM . Enjoy
pops