if we stay hotel nearby the Guangzhou East Railway, how do we go to Pearl River?

You can take local subway line 3 to reach Zhujiang New Town and then take a taxi to reach Tianzi Wharf to take the cruise.
Or there is more cheaper method for you. You can take subway line 3 to reach Tiyu West Road and then change to Gongyuanqian Station. Then change to line 2 to Haizhu Plaza. Getting out of the station from Exit A and then walk along Yanjiang Middle Road to reach the wharf.