I have to say matchFWD (http://matchfwd.com/employers). We have some solid traction and engagement within Montreal tech community. And (surprise) we're based on Montreal.
The NextMontreal blog and TechVibes are probably two other good places given their targeted traffic but I've never used it myself.
Disclaimer: I am one of matchFWD co-founder.
I recently started a list of Montréal startups built in Montréal. Not very polisehd yet but it's a start.
It's a list of companies building great online products in Montreal and meeting the following criteria:... (more)