HI, Ketchikan do your own thing, its OK to walk around - Juneau is a whale watch tour must see and the one you can book with celebrity is well worth it, book before you depart though as it gets full. Sorry we did not stop at Sitka .
Ketchikan is an easy walk around. Sitka likewise - small place. Juneau - try to see the Mendenhall Glacier if it's good weather. Mercury is a good-sized ship - we just went on it on this same trip 20-27 July 2008. It's an elegant ship and we had no idea where the other 1869 passengers were except at the lunch time buffet. The ship absorbs people remarkably well and it never seemed crowded. We enjoyed it immensely. Service and food was of the highest quality.