Princess is absolutely wonderful in ALaska...Just being in Alaska is a totally different feel in the cruise no matter what ship you are on. Food on Princess I thought was a bit better than Carnival and I love the 24 hour HOrizon Buffet. It is also very good for dinner if you miss you dinner time.
Service was excellent along with the entertainment, although compared to Carnival, they have a more lively kind of entertainment. Be sure to attend the Champagne waterfall on one of the formal evenings, check the Princess platter for day and time.
I think you will find it quiet at night compared to Carnival, but still things to do. Also, when cruising in Alaska, most days you will have excursions at the ports, so you won't be up that late.
I bet you absolutely love your Alaska cruise... Which ship are you booked on? What port do you sail out of too?