I'm reading a story where the main character debates whether he should call an cafe owner マスター or ご主人. At first he says the former doesn't fit this person, so he uses the latter, but after a conversation the owner asks him to use the term "マスター"
I looked up these two words in a dictionary, and マスター seems to correspond to "barkeep" or "master" and "ご主人" with "owner". However, none of these words in English are something you commonly use to address someone when speaking to them.
If someone can tell me the nuance between these two words, and any suggestions to map these to appropriate terms in English, I'd appreciate it.
(The story is here if you want to see the context)