The top contender according to some publications is the Archbishop of Vermont (Burlington), Archbishop Salvatore Matano. Archbishop Matano was a colleague of Archbishop Burke and they were classmates in Rome at the Gregorian University. Both are canon lawyers. Archbishop Burke's recommendation certainly wouldn't hurt his chances.
Other names that have surfaced in the press (speculation, only!) are Tucson, AZ, Bishop Gerald Kicanas, Bishop George Murry of Youngstown, Ohio, Bishop Robert C. Morlino of Madison, WI, and Auxiliary Bishop Salvatore J. Cordileone of San Diego.