Thanks for your question.
Please check following information for public transportation from Guiyang to Guangzhou, hope it will help you.
Plane: 1 hour and 20 minutes
Train: 20-22 hours (overnight train)
Long-term Express Bus: 16-18 hours
As a travel agency, we glad to arrange tours in Guiyang and Guangzhou if you need. Please feel free contact me at firstname.lastname@example.org any tim.