So here are the 50 largest metro areas in the US. Bolded are metro areas without a MLB team.
If is interesting to note that the smallest markets tend to be old rust belt areas that used to be some of the biggest cities in the country. The potential vetoes are also listed, although not sure San Antonio or Austin is a viable veto.
If MLB is looking for an east/west expansion, Charlotte and Portland make a lot of sense.
1. New York/Newark/Jersey City, NY-NJ MSA - 20,112,448
2. Los Angeles/Long Beach/Anaheim, CA MSA - 12,844,441
3. Chicago/Naperville/Elgin, IL-IN MSA - 9,434,123
4. Dallas/Fort Worth/Arlington, TX MSA - 8,477,157
5. Houston/Pasadena/The Woodlands, TX MSA - 7,904,627
6. Atlanta/Sandy Springs/Roswell, GA MSA - 6,482,182
7. Washington/Arlington/Alexandria, DC-VA-MD-WV MSA - 6,465,724
8. Miami/Fort Lauderdale/West Palm Beach, FL MSA - 6,391,072
9. Philadelphia/Camden/Wilmington, PA-NJ-DE-MD MSA - 6,329,118
10. Phoenix/Mesa/Chandler, AZ MSA - 5,228,938
11. Boston/Cambridge/Newton, MA-NH MSA - 5,034,221
12. Riverside/San Bernardino/Ontario, CA MSA - 4,769,007
13. San Francisco/Oakland/Fremont, CA MSA - 4,630,041
14. Detroit/Warren/Dearborn, MI MSA - 4,390,913
15. Seattle/Tacoma/Bellevue, WA MSA - 4,161,883
16. Minneapolis/St. Paul/Bloomington, MN-WI MSA - 3,790,295
17. Tampa/St. Petersburg/Clearwater, FL MSA - 3,418,895
18. San Diego/Chula Vista/Carlsbad, CA MSA - 3,282,248
19. Denver/Aurora/Centennial, CO MSA - 3,092,037
20. Orlando/Kissimmee/Sanford, FL MSA - 2,957,672 (Tampa veto)
21. Charlotte/Concord/Gastonia, NC-SC MSA - 2,938,830
22. Baltimore/Columbia/Towson, MD MSA - 2,857,781
23. St. Louis, MO-IL MSA - 2,814,421
24. San Antonio/New Braunfels, TX MSA - 2,813,140 (Rangers/Astros veto)
25. Austin/Round Rock/San Marcos, TX MSA - 2,620,945 (Rangers/Astros veto)
26. Portland/Vancouver/Hillsboro, OR-WA MSA - 2,542,282
27. Sacramento/Roseville/Folsom, CA MSA - 2,477,274
28. Pittsburgh, PA MSA 2,421,992 - 2,457,000
29. Las Vegas/Henderson/North Las Vegas, NV MSA - 2,407,226
30. Cincinnati, OH-KY-IN MSA - 2,312,858
31. Kansas City, MO-KS MSA - 2,270,682
32. Columbus, OH MSA - 2,242,028
33. Indianapolis/Carmel/Greenwood, IN MSA - 2,205,695
34. Nashville-Davidson/Murfreesboro/Franklin, TN MSA - 2,197,416
35. Cleveland, OH MSA - 2,165,775
36. San Jose/Sunnyvale/Santa Clara, CA MSA - 1,984,473 (Giants veto)
37. Virginia Beach/Norfolk/Newport News, VA-NC, MSA - 1,797,213
38. Jacksonville, FL MSA - 1,785,500
39. Providence/Warwick, RI-MA MSA - 1,708,161
40. Raleigh/Cary, NC MSA - 1,595,720
41. Milwaukee/Waukesha, WI MSA - 1,575,010
42. Oklahoma City, OK MSA - 1,512,813
43. Louisville/Jefferson County, KY-IN MSA - 1,402,509
44. Richmond, VA MSA - 1,389,338
45. Memphis, TN-MS-AR MSA - 1,341,412
46. Salt Lake City/Murray, UT MSA - 1,308,377
47. Fresno, CA MSA - 1,203,383
48. Birmingham, AL MSA - 1,197,766
49. Grand Rapids/Wyoming/Kentwood, MI MSA - 1,183,645
50. Hartford/West Hartford/East Hartford, CT MSA - 1,171,426