I would take that study with a grain of salt, because Toronto and Montreal's city limits now include vast swaths of older suburban areas, which offer very large lots and nice houses.
I know for a fact that in Toronto's case, the inner city is seeing a rebirth of families with kids, and it is in fact the older suburban areas that are seeing families flee to the outer suburbs. Often this is because people can get larger homes for a cheaper price in the outer suburbs.
So I don't think people should look at this study as people are shunning the city lifestyle. In most cases, people living in the new suburbs, actually have smaller lots and more dense housing than if they opted for the more close in older homes.
It basically does amount to cost, at least in Toronto's case. In Montreal's case I think it has more to do with Montreal having a lot of multi-family houses. When I was on a tour last year for school in Montreal, the lady talking to us about urban planning issues said that hte multi-family houses really does increase the amount of people that leave the core once they have kids.
Where in Toronto, most of the inner city housing is single family homes. So there is not as much of a reason to flee, unless you can't afford the $700,000 price tag for the home
But overall, many people just always are looking for the new and think it is better. We know someone who passed up a really really nice house in my subdivision with a huge yard, lots of room, and only 5 minutes from their work, for a house which is 45 minutes away from work, has almost no yard space, and is in a much denser subdivision on the edge of the metro region. They did this because they felt it was more classy to live in a new area on the edge, than in a suburb that is 40 years old. So new sells in a lot of cases.
And another reason is older residents just are not selling. Try getting into my subdivision and you could wait a while, as people have been here for 30 or 40 years and they are not planning on moving. This means no room for new families. And the couple houses that have been sold, have sold for almost $500,000, and they are not large homes. For that price people can get a house double the size, 20 east of here. But they also don't have the features my area does, like having a major mall 5 minutes away, 24 hour bus service, two hospitals 2 minutes away, a university campus and a college campus 5 minutes away, or a subway station 5 minutes away. You pay for that. Not to mention the people in the outer suburbs pay a mint to travel into the city everyday for work. Transit passes in the outer burbs can cost anywhere from $250.00-$300.00 a month. Plus your car expenses.