Stats Can population by CMA (Census Metropitan Area). Census Metropolitan area: a very large urban area (known as the urban core) together with adjacent urban and rural areas that have a high degree of social and economic integration with the urban core.
For 2005:
Toronto 5,304,100
Montréal 3,635,700
Vancouver 2,208.300
Ottawa–Gatineau 1,148,800
Calgary 1,060,300
Edmonton 1,016,000
Quebec 717,600
Hamilton 714,900
Winnipeg 706,900
A population of 1 million seems to be the base minimum. Another factor would be economic performance and the corporate sector. Quebec, Hamilton and Winnipeg do not make it.
If you look at the cities the NHL has expanded/relocated into in the US, they have the population and the economic base the NHL is looking for. Of all the pro sports the NHL targets the corporate sector and has the highest per capita income of bum in the seat which is why the NHL does well on in arena sponsorship.
2004 numbers ranking the top performing cities in the US:
http://bestcities.milkeninstitute.org/
Phoenix has a population of 3,593,408 and ranks number three in economic performance in the US.
Raleigh/Durham/Chapel Hill NC has a population of 1,294,691 and ranks number 34.
Columbus has a population of 1,597,271 and ranks number 138.
Tampa-St. Petersburg-Clearwater has a population of 2,531,908 and ranks number 12.
Denver has a population of 2,248,014 and ranks number 130
Nashville has a population of 1,288,051 and ranks number 30.
San Jose has a population of 1,678,421 and ranks number 147.
Minneapolis-St. Paul has a population of 3,083,637 and ranks number 82.
Quebec City, Hamilton and Winnipeg would not be a blip on the radar screen compared to these cities and there are a number of other US cities on the NHL wish-list long before them such as Houston, Kansas City or even Las Vegas.