a week in Montreal with my 17 y.o. son
Since I don't know where you are from, I'm not sure what your tastes are like ...
Firstly, as I have mentioned in other posts, the 'sweet spot' is to go for lunch specials at expensive restaurants around St. Denis. The worst thing you can do is go for breakfast, it's Montreal's weak link. By the standards fine restaurants are held to, Montreal's best breakfast places are expensive with so-so food and slow service. So slow that you are better off making breakfast yourself.
For a list of good expensive restaurants to visit at lunch cheaply, you can easily browse through this message board.
IN ADDITION, try Pizza at Amelio's (near McGill University), Poutine at Lafleur's (St. Denis) and Indian Food on Maision Curry Golden on St. Laurent (corner Fairmount, don't confuse with similar nearby Indian place). At the latter, you MUST order nan and (preferably) the butter chicken.
That should keep your 17 y.o. happy.