When are you coming to North America?
If it is in August then you can pick any city that has been mentioned - I am not biased - depending on whether you like a big city or you would like to explore outside these cities.

If you are coming in September I will give Quebec city a try - you can go further east towards Baie St Paul and explore a bit the northern part of the St Lawrence river and even visit ile d'Orleans whilst you are in Quebec. Vancouver will be my other choice .