Great question. Canvas doesn't have way to import a .doc or .docx or Google Doc and convert it automatically to a Quiz. Canvas does accept QTI files, which create quizzes. However, to create a QTi file is a pain in the butt. I've heard that Respondus and ExamView can convert a WORD document into a QTI file. However, it's not free, but perhaps your institution has access and you could use it.
Otherwise, you could always just create the KEY with numbered questions and then continue to use your WORD file printed or made available and ask the students to enter their scores into the quiz. I've done this before in my high school class. It worked better actually just having them record answers on a sheet of paper, then at the very end opening Canvas and entering their answers into my blank quiz, which then I had keyed with the answers so that Canvas quiz did all the scoring. This seemed to be a quick way to get results.
If you find a more effective and free way to create QTI files, please let me.