CaptJ,
You ask why I think Montreal is a poor comparison. Montreal is not one of the small number of "world cities" and for many years the local economy was stagnant with major financial services companies moving away (to Bay Street in particular) as a result of the Quebec language laws. The local geography - especially the fact that Montreal is on an island - militated against Mirabel's success. Affluent residents in West Island communities such as Ste-Anne-de-Bellevue and those living farther west in places like Hudson and St-Lazare found getting to Mirabel a pain in the neck, especially in bad winter weather.