I'm a South Indian and I live in Toronto. I was in St Jean for 8 weeks and was dying to get a taste of home. My friend recommended Thanjai restaurant. I thoroughly enjoyed the food offered at this place and left with a big smile on my face.
I had:
Sambar Vada
Masala Dosa
Gulab Jamun
This all costed around 17$ which is an amazing deal. The food quality is top notch and if you are a South Indian looking for some food in Montreal, this place is as authentic as your local dosa joint in Chennai.
I also took one of my buddies who's of Caucasian descent m. He was initially worried about the spice as he'd never eaten Indian food before. His verdict was that the food was very well balanced, savoury and not at all spicy. So if you're anxious about dabbling into the Indian cuisine, don't worry, this place isn't going to set your mouth on fire.
The quantity of food is also very reasonable at this place. The only thing I would advise you to do is to make a reservation. I spent the day in Montreal and reserved a seat, in advance, on their website and boy was I glad. The place isn't very big and seems to attract a lot of people so do beware that if you don't reserve, you may end up waiting upwards of 20 minutes.
PS: this is my first review.