Teams that could be looking for a 3B at the trade deadline:
Yankees
Twins
Marlins
Mets (if they decide to be buyers)
Phillies
D'Backs
Dodgers (maybe)
Yankees are a team that could afford Arenado past this season. Also, would include the Mets, Phillies and possibly the Dodgers, since they have big wallets. Phillies have Bohm who has been decent at 3B, though Arenado definitely is an improvement all around. Yankees and Dodgers could be interested though they both likely want to save money to make a big offer for Ohtani, so they might be hesitant taking on Arenado's contract.
The other teams like the Twins, Marlins or D'Backs likely would prefer Chapman given there is no long term attachment past this season. Chapman would be a great fit either with the Marlins or D'Backs at 3B, and would be traded out of the division and league which is also a plus.