For Montreal, I was thinking of using the Regional County Municipalities as the country equivalent. The ones that have more than 50% of the urban population in Montreal's urban area are:
Montreal
Laval
Longueuil
Les Moulins
Therese de Blainville
L'Assomption
Deux Montagnes
Mirabel
Vaudreuil
Roussillon
Lajemmerais
For a total population of 3,623,511. These would be the core counties. The next step involves using this
http://www12.statcan.ca/census-recen...ID=0&PTYPE=889
... to determine what the outlying counties are. This is pretty time consuming. La Riviere du Nord (St Jerome) and La Vallee du Richelieu (Beloeil, Chambly) would most likely get included, and possibly several others. You need to look at all of the census subdivisions within these census divisions to find out what percentage of the census division commutes into Montreal's core counties. If it's >25% the census division is part of the MSA.
EDIT: Vallee du Richelieu, Beauharnois-Salaberry, Haut-Richelieu, Jardins de Napierville and Rouville all qualify as outlying counties, some of them just barely (Maskoutains and Pierre de Sorel don't qualify, and I assume neither does Haute-Yamaska and Brome-Missisquois). Now we just need to find out the North Shore outlying counties and then we can start looking at the CSA. I'm expecting around 4.2 million for the MSA and a bit over 4.5 million for the CSA based on the commuting stats so far.