The best place for James to play would either be in Golden State or Boston. Either team would give him the best chance at titles for the next three years. If Cleveland were to do a sign and trade, there is little incentive unless they are getting a fairly significant package in return. I think something like this would be fair: Irving, Brown, Sacramento pick for James (sign and trade agreement).
I think a team of Rozier, Hayward, James, Tatum, and Horford will be the favorites to win the east and be a legitimate threat to Golden State. I'd really like to keep Brown in this scenario and, if he could be kept, I think that makes the Celtics the title favorites for three years in a row. Cleveland should push for both Irving and Brown, however, as this gives them two all-star quality players, in addition to Love and the lottery pick they own this year plus the Sacramento lottery pick next year that Boston would trade.
This is a package I think would make sense for both teams.