Single or multiple entry for China, in Seoul S-Korea for Canadian Citizen

Hi, I am a Canadian citizen and working as an expatriate in Seoul, Korea for past 2 months. I have Korean Alien Registration Card. My assignment here in S-Korea is for 1 year. I am planning to travel for my vacations on Sep 18 and visit many countries. I am considering Shanghai as my first stop from Sep18 to 22 for which I need a Chinese Visa and similarly may wish to make a stopover in Shanghai on my return to Seoul.
I would appreciate it if you could advise me, where I should apply for the Chinese single or multiple entry one in Seoul and the corresponding fee for it for Canadian citizens.
Regards,
Vijay K Chopra