Yes Rue Viau is just off Notre-Dame which is the main road running north out of the city centre down the side of the river to the port area. So long as you’re not carrying hazardous its easy. As you say, cross the border and head north up the 15, then take the Pont Champlain over the river and then bear right and follow the signs for Centreville/Downtown on the 10. When you see the sky scrapers etc in front of you, you’ll need to get over to the right and bear off on to the 720 which is in a tunnel underneath the city centre and where you’re not allowed to be with haz loads. Once on the 720 just stay on that and it’ll turn in to Rue Notre-Dame. Eventually you’ll come to Rue Viau which you’ll turn left on to. According to google earth its got a timed truck restriction except for deliveries so you’ll be fine with that.
Alternatively. When you come over the Champlain bridge on the 15 just carry on until you get to the 40. Take the 40 towards Quebec city and then exit directly on to Viau from the other end. If you’re carrying anything hazardous this would be the way to go as Montreal’s two tunnels are off limits. The Lafontaine on the 25 and the Ville-Marie on the 720.
I dont mind Montreal, though I shudder to think how your truck will cope with its automatic emergancy braking gismo as you’ll undoubtedely get cut up dozens/hundreds of times before you make it out!