The days of your grandparents finding work by just showing up at an office to fill out paper work is gone. No one just gets hired off the street for just showing up these days. Every job requires an interview, the employer has to know what kind of person they're going to be paying and having on site. Go through as many mock interviews as possible and prepare for the tough questions, it's mostly to test your customer service and problem solving skills. If anything I recommend trying Durham Youth Unemployment Centre on Bayly by the go station. However at this age with low experience and still being a student you can't expect to get a much higher wage for just a summer job that's going to be very tough.
It's helpful at this age when you're still in school.
Look for anything sales and customer service related.