My wife is from the Northumberland shore of Nova Scotia. On a clear day, you can see PEI from their cottage. I've done a bit of fishing while there but most of it was in the salt. I'm not sure if there is enough fresh water on PEI for decent Atlantic fishing. I know the northumberland runs come in when the first fall rains raise the river, similar to fall salmon here.
I don't know what time of year you're going to be there but I would think the smaller PEI waters would be more of a brookie show, or maybe sea run browns if you time it right.

I prefer to spend my time there skindiving. The water on the northumberland straight gets over 70 degrees in the summer. Also digging Quahogs while skin diving is kind of fun. You don't need a license to do so in Nova Scotia. Hope that's of some help.