Dogs and fishing.. This somthing i have a little bit of experience with.
Jack russels are some times reffered to as a fishermans friend but i think it's more to do with the fact they seem comfortable on boats and they can keep a large vessel somwhat rodent free. They are to hypo on a bank and chase your bait or lure when cast out. A bloke i know takes one fishing often and he drove me nuts.
I had a Lab as a kid and while he was more than keen to go fishing he spent more time in the water than out of it making fishing hopeless if not impossible.
My Ridgeback would sniff around for a while and then sit patiently waiting for his chance to steal my bait or catch. He was far easier to take fishing than the other 2 breeds.
I reckon a bigger breed that isnt keen on water and will want to relax while you do to would be a ideal fishing companion. I'm hoping my Bullmastiff will be like that when he gets older.