Most ships have limited smoking to small very defined areas which you should find easy to avoid. No smoking is allowed in any restaurant, on any ship. You do not say if you want to go on OV1 or OV2. Their ships are different configurations and I have only been on OV1. I say this because on OV1 the Oval bar is smoking and unless you go out on deck you would not be able to avoid smoke if you walked through the ship on that deck level. However you can avoid this by walking through (from one end of the ship to the other) on any other deck. It sounds complicated but it isnt and all smoking areas are easily avoided.
We have just returned from a Thomson ship (Calypso) and the ruling on there (and presumably all their ships) is no smoking inside the ship at all...not in the cabins or any of the public areas....it was only allowed in part of the outside deck area which was easily avoided.
We've been on both of the ships you've listed and it's pretty much the same on both, there is nowhere inside that allowed smoking on Celebration, however there was around half of the open area at the back next to the pool that was allowed and all of the open promenade. I can't remember the rules around smoking near the sun beds as we're non-smokers. Generally though don't let it put you off, the cruises are fantastic and even in the open areas it is generally far less smoky than even the beach as people who avoid smoke ourselves I can say you hardly notice anyone doing it except where there is an obvious cluster of smoking allowed tables outside.