We just did 3rd week in Sept. and found it light jacket weather with only light drizzle in Juneau (locals said you hardly ever see a full sun day there). The Glacier Bay was wonderful! We also had "cruise" freinds that did same route 1st week in Sept. and said it was "sun all around". As for animals...your chances are good anytime, as long as you take an excursion.
Pacific Princess Sept/01 - Family in Pacific Northwest
RCI Radiance Of The Seas April/06 - 25th Annversary in Panama Canal
HA Volendam Sept/06 - Dad's Surprise in Alaska
Crown Princess April/07 - Fun In The Sun in Eastern Caribbean
RCI Brilliance Of The Seas March/08 - Here We Go Again
RCI Vision Of The Seas Dec/08 - Joining Sis On Her Redneck Honeymoon in Mexico