Restaurant Keung Kee is arguably the most authentic Hong Kong place in Montreal. Unfortunately, that's also why it's not the best place for people who are unfamiliar with that style of food and decor.
I have lived in Hong Kong for 1/3 of my life, and Keung Kee reminds me of the typical restaurants there. The chef is able to reproduce a lot of the tastes and flavours I'm accustomed to eating in HK - often giving nostalgia a tickle. They also have a pretty decent selection of dishes there.
The staff and decor are reminiscent of HK as well. The staff do not speak French, and, in fact, hardly speaks English at all. They are neither rude or friendly, which is typical of Asian restaurants. The decor, with its colours and oversized drapes, are very much like the ones you would find in HK.
I wouldn't normally recommend this place to the average Joe. However, if you're feeling particular adventurous and are eager to try out a really authentic HK restaurant, then this place is for you.