Guangzhou East Train Station has direct trains to Kowloon, Hong kong. This is the fatest and easiest way, but a bit expensive, CNY190 for 1.5 hours or so. The other option is to pat for the bullet train from Guangzhou to Shenzhen, 75/85RMB for one hour and then pass the border through Luohu to Hong Kong side. Then take bus or MTR to Hong Kong, 33HKD for 45 minutes to Hung Hom. This is a good way to save some money but also fast. You can go to Yuexiu Park area. There are Guangxiao and Liurong temple, Museum, close to Beijing Road and Shangxiajiu. Then see Shamian, have a night cruise on Pearl River. I think two night at Guangzhou is enough.