This is lookout #2, but also the best lookout on the mountain. Caveat: it is only accessible by foot! I give you the address of the location of the entrance stairs. Just follow those stairs and path to go up to the Mount-Royal Chalet [there are bathrooms, water fountains and vending machines up top. Also a small café.]
The view here is the best. You see downtown, the old port, Old Montreal, the main bridges that connect it to the mainland -- a good overview of where you are: an island on a river.
1130 Avenue des Pins, Montréal, QC H3G 1A1, Canada