I think both "boy" and boo-ey, rhymes with "chop suey"(isn't that how Jim Bowie/Bowie knife was pronounced, not like David Bowie?)are used in America.
I grew up in New York and always said "boy" -as a youngster as well as now, and I remember that's how Ed McCurdy (Canadian if I recall correctly) pronounced "buoy" in the Eddystone Light, rhymes with "ahoy". So I was really surprised on a sailing course at Long Island (NY) this summer to hear everyone saying buoy the chop suey way. It sounded really odd to me!