I am in Guangzhou for 6-8 hours (in transit). What is the best way to see city in a short time?

Well, I am afraid that the tourist sightseeing bus is not the best way because they stop quite frequently. You are advised to travel around by yourself.

From CAN, take shuttle bus line 5 to Haizhu Square. Then, you can see the nearby Haizhu Square, Pearl River, Beijing Road Pedestrian Street, and Canton Tower. Have a good time!