As a bond with you and your husband, German seems to be the best medium. You can try using Cantonese with your baby and ask your husband to use German. If you just expect your baby to be able to speak Cantonese, this arrangement should help. You can let your baby learn German and English in school if such a school is available. As for Chinese, Putonghua would much better than Cantonese in terms of usefulness in the future.
Most babies can handle two languages used their moms and dads quite well. Don't worry too much.