"Bow" is the correct pronunciation, in my opinion.
"Beau" is a French term, and it means "handsome." In the French language, it is pronounced "Bow." Therefore I pronounce it as "bow."
Surprised, at how some players say this.
Plus it depends how you pronounce 'bow'.
Bow as in bow & arrow or a ribbon in the hair tied into a bow; or bow as in how Japanese people do on greeting.
So more clearer I suppose is to consider it is pronounced 'bo' (as kayleee says).
Bow (like snow, go, low, etc) because the names origins suggest that would be how it's pronounced, and it appears to be the most popular pronunciation here as well. Could be wrong though!