It has been speculated that Scopper was Sanji’s counterpart because he was the third figure in the Metal Trio of the Roger Pirates and Sanji is the third strongest in the Monster Trio of the Straw Hat Pirates.
However I think there is another connection in Gaban’s name. Scopper Gaban’s name is based on this guy:
Space Sheriff Gavan (宇宙刑事ギャバン Uchū Keiji Gyaban)
But how does he fit Scopper.
1. S stands for Space
2. Copper is another name for the police fitting the sherrif theme and Gavan has an alternate translation as Space Cop Gabin. In Australia where I live Copper is a slang for police officer.
3. Gaban is actually meant to be Gavan because the Katakana is the same for both Space sheriff and Scopper.
So I believe that Scopper Gaban is actually Scopper Gavan. Who is based on a Tokusatsu series (similar to Sentai) and who has connections to the Power Rangers in the Straw Hats?
The only thing up for debate is how strong prime Scopper was. I personally think if old Rayleigh was able to stall Kizaru then prime Scopper should have been Admiral Level.
So summing up the connection between Sanji and Scopper
1. Scopper is the third member of the Metal Trio just like Sanji is the third member of the Monster Trio.
2. Scopper seems to be in high authority on the crew given how he put Buggy in his place which Rayleigh also did. Sanji is the Military Strategist/Advisor of the Crew due to the recent revelation in the Vivre Card Databooks, alongside Luffy the Captain and Zoro the Vice Captain also confirmed in the Databooks. So Sanji is the third in command. (Only Zoro and Sanji were given positions in addition to their current roles on the ship). This parallels Rayleigh and Scopper being in command below Roger. I wouldn’t be surprised if Gaban was the Advisor to the Pirate King.
3. Gaban’s name is based on Space Sherrif Gavan who is the main character in the Tokusatsu series Metal Hero and we know Sanji has connections to another Tokusatsu series Super Sentai and Kamen Rider.
So Sanji is the Scopper to the Straw Hats just like Zoro is the Rayleigh to the Straw Hats.
*Theory by Mr.Prince of all Saiyans