Chinese double-entry visa as a Canadian tourist in Tokyo

Hello,

I will soon be visiting Tokyo using my Canadian passport. Later in my trip I plan to fly to Beijing in order to make a trip to North Korea, returning to Beijing about a week later. As I understand it, this means I will need a double-entry visa. Will I be able to apply for this through a travel agency in Tokyo? Also, will I need to show documentation of my bookings for travel into and out of China, or is this not necessary? My trip to North Korea is being organised by a tour group agency who will be making the train bookings on my behalf. What other information will I need to provide?

Many thanks,

Morgan