Josephine has a very mild Southern accent.  

Because she's African-American, I would prefer she be played by an African-American voice talent.  

Josephine used to be a singer and actress, but now she's a military leader.  She can be glamorous and playful or she can be commanding.  She also speaks French in later episodes, so someone who can speak or fake their way through some French 101 lines (e.g. "hello" "how are you?") would be good.