Montreal is generally really safe. I've been out and about past midnight a few times and never ran into so much as an unpleasant encounter. Of course it's summer, and people are generally out in the streets, but my experience has been good so far. Of course you do have to watch out for homeless people, who are usually out at night, most often drunk and they can get a bit agressive when begging for money. It's never a good idea to wander around late at night in a big city.
I've been told by locals here that the Northern parts of Montreal are less safe than other areas, and there are some parts of the city itself which are best avoided, although I'm not too sure what they are.
There are a lot of nice neighborhoods to live at, but I would suggest getting as close to Downtown as you can afford, at least until you get to know the city and find a permanent job, according to which you can rent a more permanent place. Downtown rents are really expensive though. And it really won't take too long to know your way around Montreal, the metro and bus system is so easy to learn and use.
i will move to ontario to stay close to her 8)
