I always use US currency in Tijuana, but I'll be making a trip to Montreal at the end of April and plan to take Canadian currency with me. Last week I stopped at my local bank (Suntrust) to inquire about their process. They charge a flat conversion fee of $10 for any amount I want to exchange, and asked that I give them three or four days' advance notice. Seemed reasonable and convenient to me. And worth it not to use US dollars because of the current rate of exchange and the fact that, as davephx pointed out, with US dollars "you will pay about 25% more since they usually just take it at par."
In my limited experience several years ago, the downtown Montreal clubs were relatively low mileage. However, escorting is legal there, and they'll come right to your hotel. I spent about an hour last week browsing the online escort directories, and the choices looked amazing. "Hmm, maybe I'll take one of those, and one of those, and OMG, that one for sure..." The listings in the directories usually spell out the girls' services quite explicitly (the services can vary a lot), and many list their hourly rates -- some in Canadian dollars and in US dollars. Others say "Contact for rates." Most of the rates listed looked quite reasonable, and some were less for an hour than what you'd pay for a 30-minute VIP at Follies. Have fun!