Do I need to get the visa to China again in Guangzhou?

Hello, I have a one time entry one to Guangzhou China. Then I will fly from Guanzhou to Japan for one week tour. After I will fly back home in Vancouver. But I need to connect my flight in Guangzhou and stay there for one night. Do I need to get another visa to enter Guangzhou? If so can i go to Hong Kong to apply for a transit one during my stay in Guangzhou? Or Can I waive it if I just connect my flight there with the confirmed ticket? Thank you.