Is there a direct bus to Guangzhou Railway Station in Nantou Town, Zhongshan?

Yes, it goes straight to Guangzhou Railway Station. There is a station in Nantou Bridge (not across the bridge) called An Xun. You can buy tickets and wait for the bus here. The bus leaves from Xiaolan Station. If you want to go to guangzhou east railway station, there are some, but if you want to cross the bridge, it's also from Xiaolan Station. But it's not a through train, so I don't come to the south end specially, but you can wait in aisle 105 after crossing the bridge. Note that if this waiting place is around the Spring Festival, it is basically difficult for cars to stop, so you can only go one bus stop ahead.