According to this La Presse article, Google has opened a dev office in downtown Montreal. The article mentions that a team of 7 engineers and software developers are already working there and they are hiring some more. Finally, the article says that they might be looking to invest more in Montreal as the rumor says they are looking for commercial space for 200 to 300 employees.
Update: it also seems like Yahoo is also hiring technical resources in Montreal.
Current Google Jobs in Montreal (as of February 8th, 2008):
my company, Praized Media, is hiring as well and looking for summer interns! write to jobs AT praized.com