I don't have any personal experience with Montreal, but you can find the information you're looking for using our sister site MAPS and HOTELS.com (which was designed exactly to answer the types of questions you have above)...
1) search '5 miles' from 'Montreal, Quebec, Canada' for your dates
2) on the left side of the page use the 'Search by Hotel Name' filter to enter the names of the hotels above one at a time (after you select the first you can then type the 2nd, 3rd, etc)
3) now that you have filtered the results to the 3 hotels above, you can click the marker on the map for each (or click the hotel name from the list) to open the info bubble for that property
4) near the bottom of the info window is a link to 'SEE NEARBY Restaurants, Coffee, Bars, etc.' which will show you the WalkScore for each property and what is nearby (Restaurants, Coffee Shops, Bars, Entertainment, Shopping, etc)
5) click BACK TO HOTEL MAP to repeat for each hotel
Some quick observations/comments:
-two hotels have a Walk Score of 99 and the other a Walk Score of 100, so i suspect you will be in the 'heart of the city' and have plenty to see and do in the immediate area regardless of which one you choose
-the Sofitel and Omni are a block away from each other so little difference there in terms of location, the InterContinental closer to the waterfront
-i don't know how often mass transportation is used in Montreal, but the Sofitel and Omni are close to subway line 1 and the IC close to subway line 2
-i would eat breakfast apart from the hotel as it's usually overpriced and expensive ($25-$30 USD/pp is not unusual) and you can get a better value, and find some local gems that will offer a better value (this is just my personal preference, if you love buffets and don't mind the high price tag, by all means eat at the hotel)
So i would first figure out which places (restaurants, bars, attractions, etc) you want to visit and determine of one of the hotels above is closer than the others for most of what you want to do OR that offers easier subway access to most of what you want to do (you probably won't find one hotel that is near everything, so choose the one that is near most).
The last comment is to keep in mind that the offers above could disappear at any time, so you really want to do your research sooner rather than later to increase the chances of the one you want still being there when you're ready to commit.
Please remember to return to BetterBidding and use the PRICELINE and HOTWIRE links on the board to begin your travel purchases... or thru our sister site MAPSandHOTELS.com for your regular rate purchases.
Let us know what you decide and how it goes or how we can be of further help.