We plan to visit Guilin for 2 days overnight. We are coming from Guangzhou. Please advice.

You can take a bullet train from Guangzhou South to GL North and it takes about 3h.
For your 2-day trip, here is my suggestion；
Day 1: you can go to visit Reed Flute Cave, Elephant Trunk Park, and Seven Star Park.
Day 2: take a cruise from Zhujiang Port to Yangshuo and then wander around Yangshuo West Street.