A few suggestions. -- of course you did not mention where you are flying FROM.
1 - Think about getting there at least one day BEFORE your cruise. See Seattle or Vancouver and stay in a hotel. Avoid the risk of a delayed flight.
2 - go to many different web sites to see what kind of fares you can get using the different city combinations. You can fly into SEA or VAN, then return from Anchorage (ANC). Travel people call that an open jaw. You would probably pay way too much extra to get from ANC back to SEA or VAN. Anyways, go online and play around with pricing. Sometimes leaving on a different day can save you plenty.
3 - check with Carnival. Sometimes the fly packages they offer are pretty good, AND if the flight messes up, they take care of you
4 - do some checking, you will see some options to get from SEA to VAN... depending on your timing
Let us know what you find