[Levin]

Cantonese is only spoken by people of Guangzhou area.

No lah. Lots of places in the whole Guangdong speak Bai Hua such as Shunde, Foshan, Jiangmen etc. There are places in Guangdong that speak Teochew or Hakka instead (Meizhou, Shantou, Shanwei etc) but they are in the minority. Same in Guangxi as I know quite a few people from Guangxi. All speak Bai Hua. Then you add in that 10 million from HK where even Angmos, Africans and Indians speak Cantonese.