I am not sure Princess uses, but have you checked prices yourself? Cruise lines make an extraordinary amount of money by booking your flight! Why not check out some of the major airlines website, you can probably save $200-$400 per ticket doing it yourself. I booked my cruise thru RCCL amd save $350 a ticket. That included arriving in Anchorage and departing out of Vancouver. Plan an extra day into your trip in case their is a problem with your flight.
We are doing a week in Alaska before our cruise, and with the money we saved on air, we are spending in Denali!
Last year we flew United out of Springfield, MO. to Vancouver, took the cruise to Seward and landtour to Fairbanks and flew Northwest back to Springfield via Minneapolis and Memphis. Princess booked our flights and they were $689pp roundtrip. This year (May), we're flying out of Tampa, FL to Anchorage and then back to Tampa from Vancouver. This time the cost is $789pp (roundtrip).