The sentence is :
まあ 何人来ようが || どうってこともないがな... (|| = Column break.)
It doesn't matter how many people want to come...
I'm not sure whether the first が is the subject particle (and if it can even be used right after a volitional form) or the clause ending particle...
The way I understand it the structure is "[How many people want to come] is not something that matters." Am I right?
Bonus point : I'm not sure whether the volitional form should be translated as "want to come" or "will come" (though, from what I know, most of the time だろう is used instead of ~おう to speak of the future).