So let's start from the beginning:
だけど introduces a contrast with the previous sentence similar to
勝つ and introduces it as the subject using particle
the one who wins is
何時も adverb meaning
金太郎で: This is the part stating that it's Kintarô who wins.
で is the continous form (連用形) of the copula だ, here indicating that the sentence isn't over yet.
大きな体の熊さん: "Mr." Bear's big body
でも is not the conjunction
でも=but, yet, still, but the adverbial particle (副助詞)
でも=even. See these questions for more details: 1, 2, 3 If it helps, think of it as
even if it is a bear
勝てません is the potential negative form (=cannot) of
So I would conclude by saying:
Although (something), the one who victory is always Kintarô, (and) even Mr. Bear with his huge body cannot win against Kintarō.
Or a bit further from the Japanese:
But Kintarô would always win, even the Bear with his huge strength was no match for him.