Oda is 100% making Luffy's Bajrang Gun clash with Akainu's upgraded version of Daifunka

It's no coincidence that he made the Admiral whose is a fateful enemy of Luffy and shares the same color theme as Luffy (red) specializes in giant punches like Luffy does.

In fact I believe it won't even be Bajrang Gun but Bajrang Gatling vs Akainu giant magma fists