there are lots of gyms in Guangzhou it just depends on where you will be living Guangzhou is huge. In my experience though almost every part of town has some sort of gym (mostly Muay Thai) and most gyms will have some sort of guy to come in and teach Muay Thai, Boxing, MMA etc.. the quality of these gyms canary greatly because combat spots are on a pretty big popularity wave in china right now.
What level gym are you at and what kind of gym are you looking for?
If you want to find a gym with bags and guys to spar that's to going to be too hard but if you are already a competitor that will be harder.
Edit: why Guangzhou or Foshan? if you have the choice within Guangdong i would recommend Shenzhen followed closely by Zhuhai.
Shenzhen is just way more convenient then Guangzhou, it is connected by rail to a lot of great places and the subway goes to HK, also the airport is pretty convent for International and domestic travel.
Zhuhai because it is not as big and densely populated as the rest of the major cities in Guangdong and it is super easy to travel to Macau from there. Plus the Zhuhai railway is pretty convent to go to Southern china (Guangxi, Yunnan, etc,.)