P&O dont advertise any excursions that include fishing however you can get easy access to rocky fore shores in the fiords. I never seen any proper tackle shops in the smaller ports but you could find peeler crab and limpets easily enough and you dont have to cast far to find deep water. Eidfjord has a salmon river running out into the fjords but I believe you need a licence. You may need a licence to fish from shore too. Google "Norway+fishing for rules and regs. P&O will not allow fishing around the jetty or over the stern rail but it would be easy. Like shooting rats in a barrel. Good luck.
P&O do offer a fishing excursion, at least they did on our Oriana Fjords cruise in July. It was from Olden and it was called Fjord Fishing. It was a 3hr tour: "Here's your chance to try to luck at fishing in the Nordfjord. All of your equipment will be waiting for you - fishing for trout, char and pike - plus a great variety of others." It's fishing from a boat. The cost was £40. I hope this helps.
We done the fiords on Artemis in late May/early June so I guess it depends on which ports you visit. Eidfiord, Skjolden, Bergen and Stavanger didn't have any fishing excursions advertised. Some weeks before you go P&O will send you an excursion brochure relevant to your itinerary and you will be able to know for sure from that.
I cruised aboard the Oriana this summer to Iceland and the Norway and P&O offered excursions to go fishing in the fjords. However they were on the expensive side.