What can we do for approximately 3 hours while we wait at the airport? Is there a tour that we can get at the airport and will also take us back?

Where are you going to and from?

Where will your luggage be and will you have to check it again?

Are you flying into the US from abroad?

If the answer to question 3 is yes, you won't have time to leave the airport.

end of cruise into Seward and will pick up plane to Florida at the Anchorage airport

Don't know if we can check our luggage several hours before the flight

Some airports have short tours that one can get right at the airport

The drive from Seward to the airport is 2 1/2 hours. So depending on when you get off the cruise and onto a bus you might not have any time at all to explore.

Some cruises have end-of-cruise excursions. Your luggage is taken to airport and checked thru - you never have to touch it. You get a short tour and then you get deposited at the airport. They are usually listed as appropriate for people whose flights depart later than a certain time.

Here is what I would do. Take a $5 cab ride to the Millennium Hotel. Have drinks in The Flying Machine. Watch the floatplanes come and go on Lake Hood.

Given pre-board and security, even with Pre-Check, I would not risk going further. You can also stretch your legs on the Tony Knowles trail, or go to a nearby park, for an hour or a bit more, since you are nearby.

Almost forgot the air museum, just across the road.

http://www.alaskaairmuseum.org/

xxxxxx

If you have a full 3 hours available then here's what I'd do:
- rent a car and...
- go to the Glen Alps trailhead ($5 parking if over 30 minutes). Very scenic views, and easy walks/hikes with possibility of wildlife
- next to the bridge near the parking lot of Far North Bicentennial Park (free & possible salmon spawning in stream & other wildlife)
- AK Native Medical Ctr (free during normal visiting hrs) for the best displays of AK Native arts/crafts. Take elevator to the 5th floor, walk down the stairs to each floor's landing/lobby
- Moose's Tooth for a cold local beer &/or pizza
- go home

google map link: https://goo.gl/maps/MSts5oRK5862

This is a really good/interesting itinerary.

Good luck.