Don't go on one cruise line always comparing them to a different one. Don't expect everything to be the same. Each cruise line has its own identity.
Carnival Celebration is huge and you can't possibly see or do everything in a week. There will be a variety of entertainment options competing for your time. Try to familiarize yourself with the deck plan so you have some idea where things are, particularly any of interest. Once on the ship, you can get pocket sized deck plan maps that are also helpful.
Both cruise lines are increasingly dependent on their "apps". You can still get paper menus in Carnival eating venues but they won't hand them to you be default. Just ask. Carnival doesn't put daily activity papers in the cabins these days, but they are available on the app, or you can pick up printed copies at a few locations on the ship.
The casino on Celebrity is huge with a large part dedicated to non-smoking. I think they do a fine job of keeping smoke out of the non-smoking part.