Maximum sideslipping for a multi engined aircraft usually occurs at Vmca when the pilot will have maximum rudder input that he can provide to offset asymmetric thrust.
Sideslip angles for Vmca/l and for a max crosswind are probably going to be similar. Say up to about 10 degrees. Operationally you'll rarely if ever need sustained sideslips, but the aircraft will be theoretically capable of some greater level of sideslip.