Amazon seems to want a city where they would be a Big Deal, maybe the dominant employer. In New York or LA, they'd just be another big business.
Weather is an issue. They'll want some place that doesn't flood or get snowbound, since their HQ city will include some distribution centers. That knocks out Minneapolis - St. Paul, Houston, Miami, and Tampa.
They probably don't want a super high cost area, which knocks out SF-Oakland-San Jose. Maybe Washington, DC, too.
Extreme high crime areas are out - that takes out Tijuana and Detroit.
Mass transit is a specified requirement. This takes out cities with weak transit systems.
Not too close to Seattle, since they want to be more geographically distributed. That probably takes out the West Coast cities.
So what's left?
Chicago
Dallas–Fort Worth
Toronto
Philadelphia
Atlanta
Boston
Phoenix
Montreal
Denver
St. Louis
Baltimore
Charlotte
Orlando
San Antonio
Pittsburgh
Cincinnati
Las Vegas
Kansas City
Cleveland
Columbus
Austin
Indianapolis
Nashville
I'm going to guess Austin or Nashville. Small enough that Amazon can be a big fish in a small pond, big enough to support the work force, liveable enough that people will come, good land availability.[1] https://en.wikipedia.org/wiki/List_of_North_American_metropo...