If you have friend in Montreal, you can ask him to find an apt for you.
If your friend has more than one room in his apt, you can live in his living room in first several days.
It is easy to find an apartment in Montreal. You could read montrealGazette.com, afterhour.com which newspapers have web sites. But when you have a street tour in Montreal, you can see a lot of Ad-board in front of these apartment building. It displays tel#. Sometimes the landlord office is in the building.
I live in an apt building which has a lot 1-1/2 apt. If you are interested, I will give you the landlord tel#. You give him a call to see whether he could accommodate your family.
Room type---rent fee
3-1/2 $350-450/month (one bedroom apt)
4-1/2 $400-500/month (two bedroom apt)