I am a college student from the U.S. looking to live with my best friend for the summer. He's from Vancouver. To get a Canadian work visa will I have to find an employer before I am able to apply for one, even if I only plan on getting a job in a restaurant or some place like that?

Yes you will need a work permit...the employer has to give you a letter explaining the details of the job including the salary and things like that. The letter must be attached to the application when you send it in.