If you're leaving from the Old port of Mtl you'll enjoy staying at the luxurious Delta Suites Hotel on University St Downtown . It has a revolving restaurant on the 26th floor...marvelous panoramic view of the city. I think it's about $119CAD-$1499CAD per room, depending on your taste.
You could also stay at the Intercontinental Hotel or the Hilton Place Bonaventure. Both are very nice and a short distance from the Iberville Terminal (Old Port), especially the Intercontinental. If you have more questions, don't hesitate! Nicolas