Hi drummerboy,

I think, there isn't a near way from mandarin to cantonese, the only benefit is the grammer is almost the same, so you don't need to spend much time to learn it.

So just trade it as a new language, more listening and more speaking.

(My native language is mandarin and i have been living in GuangZhou about twenty years, so i hope my answer will help you.)

Thanks, Will