It all basically will depend on the interest rates - the more they go up, the more the Real Estate market will go down. If you're buying it for a long-term investment, just wait for the right time/market to sell it. At 900k I figure you won't find many buyers for the Old Montreal district - unless they are single & very rich - which leaves you a limite market to sell it to. Double income homes with families will not be looking for Old Montreal as their primary dwelling - simply because of the human traffic, tourists & general 'deserted' feeling in the winter nights.
Interest rates are still relatively low - some families are barely making it now - once the rates go up, you'll start seeing more sellers than buyers which will make the market prices go down.
The other thing to look at is how easily will you be able to rent it should you decide you don't want to live there anymore & want to wait for 'your' selling price?
That's my 2 cents, quiet
P.S. Nun's Island has some fabulous townhouses/condos & the demand there is much higher - easier to sell short/long-term.