Hi there. I'm an American expat living in the West Island of Montreal. My husband and I moved here from Austin, Texas for his job in May, so I can answer most of your questions. We've got work permits, but are not PRs, though we'll be applying for that as soon as we're eligible next year. There really aren't a lot of people in your/our situation, so I'll do the best I can to help you. Here goes...
We're considering a move to Montreal from Phoenix, Arizona (we know it's cold up there, so are planning on moving during spring).
This is exactly what we did, and it has worked out great so far. The summer is absolutely amazing, btw. Lots of events, festivals, opportunities to get out and see the city while the weather is supremely pleasant. Fall is actually really nice as well, and the fall foliage is magnificent. And, you also get to adjust to the whole idea of winter a little more gradually.
Questions that we need answers to:
1) We have 2x dogs & 1x cat. Are there any immigration things that they'll need to go through, boarding, shots, etc.?
We drove into Canada with our 3 dogs and our SUV. We weren't hassled at the border at all; we had rabies documentation for all of them at the ready, and that was it. Bringing animals in from the US is no big deal, even if you fly them into the airport.
2) We do not speak French (yet) and want to move within commuter distance (30-40 minutes, either drive or train) from Rue Saint Antoine Ouest, Montr茅al - are West Mount or West Island within this range?
Not speaking French is a problem, occasionally. Not reading French is extremely inconvenient to possibly dangerous. Not understanding spoken French just makes interactions awkward. And constantly having to ask people to switch languages feels really rude and obnoxious. As a monolingual Anglophone, I feel kinda excluded by a lot of what is going on in the city, the local media, etc. It isn't a particularly easy language to learn, though reading comprehension is very important to work on first, since signage will all be in French. Traffic signs are in French. Menus are in French. Everything sold anywhere in the province is labelled in French. You should absolutely not move here without spending a significant amount of work learning the language. My piddly 3 years in high school hasn't helped much at all.
As far as commuting and where to live - I'd suggest the West Island. Westmont is pretty pricey, so if you're fine with a condo or apartment, or if budget for a larger place isn't an issue, than it would be fine. West Island is THE place for Anglophones, in my opinion. I'm in Pointe-Claire, but Beaconsfield, and Kirkland are all very nice and most people prefer to speak English in daily life. The commuter trains are also convenient and a cost-effective way of getting downtown. I think my husband pays around $100/month for train and metro, which is WAY cheaper than what it costs to drive. Gas is over $4/gal.
3) We have a 10th grade teen in High School, will they have any problems switching to Quebec school system - tests, curriculum, etc.
I'm not 100% on this, but I don't think your teen is eligible for schooling in English unless you get a waiver. As I understand it, the only kids who are allowed to go to English schools are those who have a parent who was educated in Quebec in English; everyone else, Francophones and immigrants, including Anglophone immigrants, go to French language schools. However, there are a number of private schools in the West Island where English is the language of instruction, and private schools are exempt from the restrictions of the language laws. I'd suggest going that route for your teenager.
4) What are the average price of a rental property per month?
We got a great deal on our house, but you can expect to pay around $1800-2000 for a modest-sized house in the West Island. There are also lots of really amazing homes as well, if you're budget is higher. I'd suggest getting in touch with Michel Fournier; he's a realtor with Remax and the one to start with if you'd be interested in Pointe-Claire. There doesn't tend to be a great deal for rent, though it can be found.
5) We have a 5 person family and would be looking for a house, 4-5 bedrooms, 2 bathrooms - prefer somewhere cottage-like with spacious yard. Are we dreaming or is this realistic in the above areas?
Actually, if you're going to find something like that in Montreal, it'll be in the West Island, but there isn't a LOT of that. There isn't much new construction, so the majority of homes are older, but have been renovated, but still don't have the spaciousness that most Americans are accustomed to. They don't really do McMansions here, by and large, though I've seen some very large (non-mansion) homes in small pockets here and there. Housing costs much more here than in the Southern US. I'd imagine you're looking at at least 3k/month for something that has 4-5 bedrooms.
6) If I move up on work visa will my wife (she is a US citizen) be able to work while we're there? Will my 10th grader be allowed to work if they reach older teens while we're in Montreal?
I can't answer about your specific situation, but I can tell you that because my husband has a work permit for his job, I was granted an open work permit. Because of my husband's special skills and the industry he's in, his workplace speaks English maybe 50% of the time, and he gets by without knowing much French. However, I can't find a job because I'm not bilingual. Nearly every job in Montreal will require you to be able to interact with both French and English-speaking customers. I have no idea if your kids would be able to get work permits, though.
7) How long do we have to reside in Montreal to be considered residents, for health-care, etc.?
3 months and then you can apply - the website you need is REMQ -
10) If there is anyone who has recently moved from the US to Montreal, specifically the West Mount / West Island areas, who could give us the low-down on what to expect I'd appreciate the inside insight!
Westmont is overly pricy, crowded, and a tad pretentious. The housing prices are unreal if you need access to a backyard. West Island is very suburban. There's the Fairview Mall for shopping, plenty of nice grocery stores, a few movie theaters, and lots of other Anglophones. Lots of old people too, though I'm not sure why that is exactly. The West Island is definitely family focused with lots of parks, libraries, kids hockey leagues, etc. It is also a reasonable commuting distance from all the stuff going on downtown as well, so it doesn't feel like we're exiled out here with the other Anglos. People tend to live where their people are. The Italians have St. Leonard and Little Italy, the native Quebecois live on the East End, and the hipsters live on the Plateau, and so on.
Montreal, and the surrounding area, looks like a 180 switch from where we're living right now and we're kinda excited about the prospect of the move. Some of the kids have not seen / do not remember the fun of snow fall and actual seasons.
I've lived in the Southern US most of my life, and some things are very different here, and others are amusingly consistent. I now know the French words for pretty much everything I eat, and yet our lawn service is still staffed by Hispanic immigrants. The food is wonderful, Canadians really are very nice people, and everybody watches the hockey games. On the downside, the language barrier is isolating and everything here costs more. But overall, it has been a good move for my husband's career, and there are good and bad things about anywhere you live.
I blog at and you're welcome to contact me if there's other stuff you're dying to know. 
Good luck.