I can't believe Atlanta is any serious discussion. I say go to KC before giving Atlanta a chance at a 3rd failure.
Houston makes a bit of sense. Wonder if you could make somewhere like Boise, ID work to try to capitalize on the rocky mountain region?
Boise is half the size of Quebec City both in city and metro populations. If Quebec City isn't making it, Boise shouldn't be anywhere near the discussion.
Atlanta is fine, but they are going to have to rebrand. The Thrashers are a tainted brand with not much of a desire to see return. It is cool and the branding was very original, but its tainted. This isn't Winnipeg where the day they left, everybody in the city wanted them back.
The biggest US markets (all bigger than all the available Canadian markets as well as Ottawa, Edmonton, Calgary and Winnipeg) without an NHL team are:
Houston, Texas (5)
Atlanta, Georgia (6)
Phoenix, Arizona (lol) (10)
Riverside, California (12) - Probably within the Kings or Ducks exclusive area
San Francisco, California (13) - Certainly within the exclusive area of the Sharks
San Diego, California (18)
Baltimore, Maryland (20) - I'm guessing is within the Caps exclusive area
Orlando, Florida (21)
Charlotte, North Carolina (22)
San Antonio, Texas (24)
Portland, Oregon (25)
Austin, Texas (26)
Sacramento, California (28)
Cincinnati, Ohio (30)
Kansas City, Missouri (31)
Cleveland, Ohio (33)
Indianapolis, Indiana (34)
I figure I'll stop there, but there are 9 NHL markets smaller than all of these. Edmonton (Would be 43), Calgary (Would be 42), Raleigh (41), Ottawa (Would be 42), Winnipeg (Would be 72), Salt Lake City (46), San Jose (36, but it has San Francisco very close), Nashville (35), and Buffalo (50).
There are a lot of options and some of them already have suitable arenas.