Looking into Kanba's feats (since I give too little of a shit about Heroes to keep up to date with it), it seems his SSJ self forced Vegetto into using SSB Kaioken, suggesting he was superior to Vegetto. Even if the two were about even, Kanba would win due to far better stamina.
I changed that to Kaio-Ken. Neither seemed really worn-out, maybe Vegetto a-bit more and Kanba seemed to have some-what torn clothes. When Vegetto said he'll get serious though so did Kanba, so maybe they were just plain even but Kanba had better stamina.
In that case, Vegetto stomps. From what I'm aware, Kanba had to go Golden Oozaru almost immediately to gain the advantage and was already about even with a version of Vegetto half as strong as this one. Vegetto will have far worse stamina, but he should still be able to finish the job before he diffuses.
Also, yeah I forgot to say this. In the manga it's hard to tell because the art, panel and everything's so sheet I can't even tell what's going-on but to me at-first it seemed like they just powered-up to SSJ-Blue full-power and SSJ because Mai and Oolong are talking and then suddenly there's this big whooosh as if there was a storm (of power) or something, but then why would Vegetto say he'd get serious straight-away with the Kaio-Ken or Kanba as-well for that matter?