You need a single entry tourist visa ahead of time, you can apply for this visa while you are in Hong Kong or in Canada. It's true that foreigners holding ordinary passports of the countries having diplomatic relations with China and on a tour to Hong Kong and Macao, and participating in group tours to the Zhu Jiang River (Pearl River) Delta Area for a stay of less than 6 days organized by the travel services legally registered in Hong Kong or Macao shall not need to apply for a visa. The Zhu Jiang River (Pearl River) Delta Area refers to the administrative area of the 10 cities below: Guangzhou, Shenzhen, Zhuhai, Foshan, Dongguan, Zhongshan, Jiangmen, Zhaoqing, Huizhou and Shantou.

But Shanghai is not included in the Pearl River Delta Area.