While Durantula is my personal favorite player, I think that the scarcity of assists puts Lebron and CP3 at the head of the pack. At the same time, that makes it less likely that you could get both.
Speaking as a guy who just traded away Lebron in a keeper league (we keep 4 - I'm picking between Durant, Brook Lopez, Kevin Martin, Kevin Love, Eric Gordon, Rashard Lewis for now) I'd say that your best bet is to target a team that's in contention to win THIS YEAR and make a Godfather offer - something that can pretty well deliver them the league title.
For my team in my league, it took Lopez, Gordon, Chris Kaman and Vince Carter for Lebron and 3 of the 4 weakest players on my roster. But now the other team has Lebron, Jennings, Al Jefferson, and Jameer Nelson.
If you can make that kind of a deal without giving up Nash, you're in great shape to go after one more, as he's the best single chip you have that you can spend. Nash and Harris for CP3 would be a great deal for you, but maybe not for the other owner - depends.