Assuming you have a debit card on the Cirrus network, you should be able to get Canadian cash very easily. You should know we have two kinds of ATMs - those associated with a bank and the so-called "White label" ones that are typically in convenience stores and hotel lobbies and charge a much higher fee. The machine will tell you the fee as part of the transaction (and you can cancel without incurring it if you don't like it), but if you seek out a bank-associated one (on the outside wall of a bank, typically, though there may be bank-associated ATMs at the airport) you will save on fees.
It would help to know a little French - please, thankyou, and numbers for speaking, more than that for reading. You will find that written signs are often in French only (eg instructions in a parking garage) which you can probably muddle through with a phrasebook as long as you have the time. Most people speak English, but the signs don't give you that impression. Service people will typically greet you either with bonjour or hello-bonjour, which can be hard to recognize as a greeting at first.
If you don't have enough French to follow a TV show in it, and you don't care about Canadian sports and politics, you are not likely to enjoy watching TV in the hotel (the channels are half-and-half English and French and the hotels seem to carry less US channels than the rest of the country), so perhaps bring a book or something else for evening entertainment.
Montreal is a great city for walking and a horrible city for driving. Bring a guidebook and go for walks at lunchtime, check out the old city, and try not to sneer at us for considering that to be old. I recommend against having an opinion on The Two Solitudes, Distinct Society, and the like. Eg don't say "weren't you guys going to separate or something?" with people you've only just met. And bring your appetite! The food in Montreal is amazing. You should eat smoked meat and bagels, and poutine, because they're iconic, but you will also find wonderful fine dining, locavore, slow food, and more.