Travelling from Canada --> Hong Kong --> Beijing --> South Korea

Hi there,
Thanks for all the information. I will be travelling on the following schedule:
November 24th (19:20)- Canada to Hong Kong
November 30th (18:15) - Hong Kong to Beijing
December 3rd (08:30) - Beijing to South Korea
Will I require a Visa ahead of time or will I qualify for the 72 hour pass in Beijing and can I travel anywhere within the city?
Thanks so much in Advance