Invitation Letter for single entry tourist visa.

Hi! My (Chinese-Canadian) friend from Vancouver is having his internship at the Canadian Embassy in China. I am planning to visit him next month and stay there for three days.. One of the requirements of a single entry tourist visa is an invitation letter. Can this come from him? and can his canadian passport work as well? Thank you! We just want to go to the Great Wall and do some sightseeing. thanks!