Hello

I am a Canadian. I wil stay in Singapore for a few months. At the end of my visit in Singapore I plan to join a tour group who will organize the tours to Chengdu and a few other cities. I want to apply for a China visa before I leave Canada. I have a return air ticket but I do not have information regarding places to visit in China or name of the tour agency. Can I apply for the visa before I leave? If so, do I apply for single or double entry visa.thank you