If you are truly into fly fishing, look at sites on the Miramichi which boasts some of the best Atlantic Salmon sports fishing. However, I believe that if you are not a New Brunswicker, you will need to hire a guide to get on the river, but there are lots of them and many hve websites, just google search them. As an alternative, there are nice sites and rivers in the Highlands of Cape Breton, Nova Scotia.
As for National Parks with electricity, I think both Fundy Park, near Moncton and Kouchibiguac not too far from Miramichi have modern facilities, including hook ups.