I would like to ask , should i need to take a transit visa?

Dear: Mr./Madam
I'm Cambodian, I would like to ask some question about Chinese Visa , i'm going to fly from Phnom Penh (Cambodia) to Istanbul (Turkey) by China southern airlines and i have to transit in (CAN) Guangzhou duration 3h 15min and in (PEK) Beijing (China) duration 2h 30min