What about Muslim in Guangzhou? Could they find any Halal food in this city?

Yes, there are many halal restaurants in that city. Here list some of it.
Muslim Restaurant, located at No. 325 of Zhongshan 6th Road.
Zhenguoyin Halal Restaurant, located at No. 4 of Tiyu Xiheng Street.
Mongolian Meishicun, located at No. 12 of Aoti Road.
Istan Halal Restaurant, located at No. 617 of North Tianhe Road.
Qinghai Musilm Restaurant, located at No. 71 of Sanyuanli Avenue.
Taoyuan Halal Restaurant, located at No. 55 of Zhongshan Avenue West, Tianhe District.