Not sure what web site you are looking at, but most certainly there are Kenai Fjord boat tours running in May. I would add as many days pre cruise as you can and get to Seward, rather than spending the time in Anchorage. Otherwise, get yourself a car rental out of Anchorage and do your touring there- if that is your priority area.
You need to do your home work and find out what is of the most interest to you in the areas. Then make your location choice
www.anchorage.net www.seward.com