If you hope to get some fishing in here is what you will want to do...
Obviously, you can't fish from the ship, so you have to choose which port of call or stop (during you land portion) you want to use for your fishing experience. I assume you mean ocean fishing (not river) but I don;t know.
Let's say it is ocean fishing - pick the port that is most likely to be closest to the kind of fish you want to catch - say it is Juneau. Now go online and look for day fishing boat operators who will pick you up at the ship, drive you to their boat, take you out all day and then handle you catch in case you want to ship it home.
Most cruise lines will likely offer such fishing adventures, but I am sure you will save money and have a better time if you pre-arrange it.
DO look for someone who is an established operator of a boat, who does this for cruisers all the time (90% of Alaska tourism comes from cruise ships, so this is not hard to find). Look for letters of recommendation, etc.
Once you pick one stay in contact with them. Leave a deposit but do not pay in full unless you are sure they are reputable and that is their policy.
But to summarize, I am just trying to say that the best fishing arrangement will likely come from a third party, not arranged by the cruise line. You can easily set this up in advance over the Internet, so I recommend that.
Other things I recommend highly in Alaska - whale watching.
You just might be able to combine fishing with whale watching - since that is another activity you will arrange on a smaller boat while the ship is in a port of call.
Please send us your ship's itinerary so we know more about where you are going. And HAPPY CRUISING!