Not really. There is overlap, but traveller implies a greater amount of effort and planning to go around the world.
Sight seeing is what you do when you have got to a place on your journey, literally looking at the scenery etc.
What is the context in which you want to use one of these?
To me, sightseers are a subset of travelers*: those whose purpose in traveling is to see the sights in the places they visit. Travel can have other purposes: to conduct business, to visit family, to study languages, and more. The word traveler describes what one does, while the word sightseer also describes why one does it.
*British English spelling uses ll; American English uses one l.