Hi amit,
I lived in Montreal for a decade (moved out of the city last year) and I can provide helpful info.
Montreal is a beautiful city. The French and English language spoken by many locals is part of the beauty that the city offers. I did my undergrad studies there and managed to work for 6 years in two different companies without speaking a word of French. However, the Quebec government does provide free French courses for new permanent residents. My stay over a long period of time helped me learn French from the people around me.
Montreal downtown is bilingual. The east end of the island is mostly French and while the west - referred to as the West Island - is English dominant. French is spoken heavily in the cities on the outskirts, such as Laval. I had hard time in my first year in Laval to get by with English only. So I moved to Montreal the next year.
MBA wise, I sat in a HEC MBA information session in 2012. The staff is very friendly and the whole program is strong - on par with Desaulets's and John Molson's. The fees are low since most of the tuition is subsidized by the government. The only reason Desaulets's is expensive is that the school decided to go private and avoid the subsidy. The university got fined by the government but it was happy to pay it and get on and fight for N.American and global rankings.
I believe if you want to stay in Montreal, HEC would be a great choice. Language won't be a problem as most likely you will be employed by a big international company whose internal communications is done in English. You will also be provided with free French courses as many companies try to encourage their employees to learn French. This is up to you and your goals. Once you hit the road running in Montreal, you can switch cities later if you decide to take a different road and build your life in another city such as Toronto, Calgary or Vancouver. Most people are attached to Montreal. It was hard for me to leave.
Overall, HEC is a good business school. If Montreal is your post graduation destination, then you are on the right path.
Good luck!