I'd pick Hamilton, Quebec City, Seattle and Saskatoon.
Hamilton could draw from about 700,000 people the metro area, plus 450,000 in Niagara, 550,000 in Waterloo Region, and another 700,000 in SW Ontario from London to St Thomas to Stratford to Brantford to Simcoe for a total of 2.4 million people, so about like Vancouver. Plus some disgruntled Leafs fans from the GTA.
Quebec City could draw from central and northern Quebec, which is maybe 1.5-2 million people.
Saskatoon could work since Saskatchewan only has 1 "major league" team (CFL Rough Riders) and they're based in Regina. Plus about 300,000 in the region, 1.2 million people total in Saskatchewan. Probably the city I'm least certain of out of the 4 though, and maybe Halifax has a better shot since the Maritimes don't have a team and have about 2 million people while AB and MB have 3 teams so Saskatoon would probably be getting fans just from SK. However I think SK is more hockey crazy than the Maritimes.
Seattle - A pretty big and wealthy city.
If I had to pick another 10 teams:
London
Milwaukee
Richmond Hill
Syracuse
Grand Rapids
Laval
Halifax
Cleveland
Portland
Indianapolis
Tongue in cheek proposal:
Welland
Bowmanville
Lloydminster
Thunder Bay
Brantford
BTW I wonder how many of the fans in Phoenix, Tampa and S Florida are Canadian retirees.