Sanji will only fight the "more relevant" Titanic captains, which means either Burgess Shiryu or Lafitte.
Shiryu is the second strongest so Zoro gets the job.
Lafitte doesn't have enough feats to justify him being Sanji's opponent, unless Oda wants to showcase a middiff.
Burgess have enough showing to justify him being on Sanji's level. Besides, his new DF is now "countered" and can "showcase" Exoskeleton's capabilities and Sanji's role as the "Shield".
Also, not surprisingly, Sanji's opponent won't be a speedster or a swordman, so Burgess is more likely.
Bonus point: Van Augur to showcase Sanji's CoO range (a sniper) and Sanji's speed (a teleporter).