According to Chad Ford, Kevin Love isn't the only trade option for the Celtics with the 6th pick.
I think the Cavs' preferred route would be a trade that thins out their roster and adds a young veteran who can immediately lift the team's long-term chances. The Minnesota Timberwolves' Kevin Love has been the most mentioned pickup. But the Cavs also have their eye on other bigs, including the Chicago Bulls' Joakim Noah, the Portland Trail Blazers' LaMarcus Aldridge and the Atlanta Hawks' Al Horford.
While the Celtics, Lakers, Kings, Hornets, Wolves and Suns aren't likely to get All-Stars for their picks, they should be able to score players or multiple assets to help their teams right now. Look for the Bucks, Hawks, Mavs, Blazers and Raptors to be especially busy trying to move up or acquire a second pick.
If the Celtics can't land Love, I wonder what else they would be looking for in return. (Note that the bigs named above are targets for the Cavs with the #1 pick. Not the Celtics or other teams. I'm not even sure if any of them is reasonable for the #1 pick.)