Translation: "7 years ago there was a guy called ‘Cell’…[Dabra]’s probably about as strong as him…”
かな: I wonder; I guess たぶん: perhaps; probably
Would these versions be just as accurate?:
A. "[Dabra]'s probably about as strong as him, I guess..."
B. "[Dabra]'s perhaps about as strong as him, I wonder..."
Both A and B are mostly correct, but are missing a little in terms of nuance.
「たぶん」implies much less uncertainty than 「かな」, so what he's really saying here is:
"He's maybe as strong as Cell, probably..."
With Goku's 「たぶん」 being a way of making his guess more firm. By saying "I guess" or "I wonder" at the end of the sentence in your translations, you're slightly removing that finality of him saying "probably."
The original has a connotation like he's saying "he's about as good as that guy, yeah, that sounds about right."
