Always when I travel I need a spot that I can use my computer - sometimes just for 15 minutes and at other times for a few hours.
Cafe Vienne at the corner of Sherbrooke and St. Denis is one of those places.
I can get an excellent cup of coffee, a pastry (or breakfast if I want - just simple stuff), it is usually quiet, there is street parking that is not too restrictive and you ask for the internet code and they give it to you. No worries if you don't speak French as they are bilingual.
It has a nice European-Montreal flavour to it.