Every time I'm in the Toronto area, I just have to go to Marathon Cafe. They are my hands-down favorite cha chaan teng outside of Hong Kong. The milk tea is an A+ in my book (rich and strong), and the food is your standard Hong Kong diner food. I love the butter and condensed milk toast, the egg sandwiches, and the soup noodle dishes. It tastes just like you're in HK!
The diner itself is usually clean but not amazingly decorated or anything, and the service is pretty standard. It's essentially a fast food diner, providing very quick and tasty meals and drinks.