I've spent two 16 day trips to Nova Scotia/PEI in the last few years and in neither have I seen half of the province. There's a lot to see, even if most of the stops are short because the things you come across are interesting and photogenic without being long term absorbing. I think you do need to choose an area, get there as quickly as you can, and stick to it.
I'd love to photograph in Newfoundland. The reason I haven't is that distances /driving times seem long and the ratio between driving and photography doesn't seem quite right to me. On Nova Scotia things seem closer together and more accessible and you certainly won't be short of pretty (and gritty) fishing ports. Personally I'm ambivalent about much of PEI and its not an area i'd want to visit in summer with lots of beach-seekers and the whole "Anne of Green Gables" thing which I just don't get. Otherwise PEI is pretty much flat or gently undulating farmland.
My last visit to NS was in fall, when the foliage is spectacular - bear in mind it really isn't along way from Acadia- and without the crowds of Vermont and Acadia. The downside is that a good part of the tourist accommodation is closed for the winter and so are many of the cafes/lunch stops. I'd have a look on flickr to see some pictures of these areas in high summer- I've been in July and found the countryside not terribly interesting whereas in autumn it can be extremely photogenic. So in summer the interest lies even more strongly on the coast.
You can see some NS/PEI photographs on my website www.photography001.com in the "new work" gallery.