Just thinking this through from a numbers perpsective
Atlanta (Mercedes Benz)
NYC (Met Life)
LA (Rose Bowl/Inglewood)
Dallas (Jerry World)
Philly/DC (Lincoln/FedEx) - Can't see them picking both, but with the 250th anniversary of 1776, one or the other will be picked.
San Francisco (Levi's)
Miami (Hard Rock)
Baltimore (M&T Bank) - Far too many other host cites nearby
Cincinnati (Paul Brown) - Immature soccer city, doesn't measure up to other major metros
Nashville (Nissan) - Close to Atlanta, immature soccer city, lower tier stadium
So that basically leaves 2-3 spots to fill from the following contenders:
Seattle (Century Link) - America's best soccer city but not many nearby venues, could be problematic for travel, but also beneficial to Canada, since Vancouver withdrew
Orlando (Camping World) - Great travel/hospitality infrastructure, but how likely are there to be two cities in Florida?
Kansas City (Arrow Head) - Mature soccer city, strongest Midwest candidate (no Chicago or Minneapolis)
Denver (Mile High) - Not much soccer culture, location could be problematic
Houston (NRG) - Only real downside is the proximity to Dallas.
My best guess is Houston, Kansas City and Seattle to round it out.