To pronounce it otherwise marks one as a native of Massholia, a state somewhat to the south. Ted Kennedy was famous for saying "Bang-ah? I haadly noo'ah."
BTW, if your friend grew up in Ogunquit, he needs your sympathy, but don't turn your back.
For 80 plus years (I’m sure for the first couple years of my life I had no reason to utter the word Bangor) I have pronounced it Bang-Gore (soft g, hard g) but whatever.