We were on the Spirit of '98 last month - May 17-25. We sailed from Juneau to Ketchikan. I think you will really enjoy the trip. The Spirit of '98 is sort of duded out as a turn of the centur steamer, in its decor. I believe that the actual layout of the ships in the fleet does not differ too much. i.e. the bridge and a sundeck on the top, a dining room and galley on the bottom deck, and a lounge in the front of the ship on one of the two other decks. We had a AA cabin and were very satisfied with it. The spirit of Endeavour is sleeker-looking and more modern in decor. They hold about the same number of passengers....around 98 or 100.
Bears. I assume you are considering a separate bear viewing trip. I don't think this was being offered as an "optional" tour on our sailing.
However, from the ship we saw bears in Glacier Bay, around Sitka, in Endicott Arm and on the way to Tracey Arm. The 'exploration directors' are very good at sightings and letting everybody know about them. Our ship had binoculars in the cabins and there were more spread around the lounge. We spent several hours in Endicott Arm, watching the glacier calve and looking for wildlife. We were put out to float around in DIBs to get closer to shore. We saw a mother bear and two cubs here, as well as mountain goats, Dall porpoises, harbor seals floating on ice floes, and a hump back whale or two.
Speaking of *optional* tours....well, first of all, the cruise includes many tours in ports. There are also some you can add on at additional cost. (called "optional".) We didn't take any flight trips over glaciers, since we had done that in Southwest Alaska a few years ago.
But, if offered, I would recommend the White Pass and Yukon railroad trip out of Skagway. and if possible the train up and a minivan back. It takes about half a day. The scenery is spectacular. Another "optional" we loved was the Raptor Center in Sitka.
You are in for a treat. If you have any specific questions about the trip itself, let me know.