Here's a deep dive on all potential big man upgrades. I was pretty loose on "all star potential"...like if everything broke right. The most easily attainable are obviously the FA, though any of them would mean no Hayward. The next most realistically attainable are probably those 5 vets though they all come with contract, injury, or performance warts.
Out of the prime/young candidates with all star potential there are probably only a few that could maybe be pried away with a significant package depending on what else happens with their team/direction:
Porzingis, Drummond, Favors, Myles Turner, DeAndre Jordan
Big Man Targets:
Trade Targets (All Star Potential Young or Prime):
Anthony Davis, Karl Anthony Towns, Kristaps Porzingis, DeMarcus Cousins, Andre Drummond, Derrick Favors, Jabari Parker, Simmons, Embiid, Myles Turner, Kevin Love, Tristan Thompson, Hassan Whiteside, DeAndre Jordan, Draymond Green, Nikola Jokic, Rudy Gobert, Steven Adams
Trade Targets (All Star Potential Vets):
Marc Gasol, Carmelo Anthony, Brook Lopez,
Dwight Howard, LaMarcus Aldridge
Trade Targets (Rotation Potential):
Aaron Gordon, Nik Vucevic, Kenneth Faried, Valanciunas, Poeltl, Saric, Okafor, Portis, R Lopez, Thon Maker, Markieff Morris, Gortat, Tyson Chandler, Gorgui Dieng, Randle, Zubac, Chriss, Bender, Len, Cauley-Stein, Koufos, Nurkic
FA Targets (All-Star Potential):
Blake Griffin, Paul Millsap, Serge Ibaka, Greg Monroe, Nerlens Noel
FA Targets (Rotation Potential):
Mason Plumlee, Pau Gasol, Dewayne Dedmon, James Johnson, Taj Gibson, Ersan Ilyasova
Toronto Raptors:
4- Ibaka
5- Valanciunas / Poeltl
Philadelphia 76ers:
4- Simmons / Saric
5- Embiid / Okafor
New York Knicks:
4- Porzingis
5-
Brooklyn Nets
4-
5- B Lopez
Chicago Bulls:
4- Portis
5- R Lopez
Indiana Pacers:
4-
5- Turner
Milwaukee Bucks:
4- Parker / Maker
5- Monroe
Detroit Pistons:
4-
5- Drummond
Cleveland Cavs:
4- Love
5- T Thompson
Washington Wizards:
4- Markieff Morris
5- Gortat
Miami Heat:
4- James Johnson
5- Whiteside
Charlotte Hornets:
4-
5-
Atlanta Hawks:
4- Millsap / Ilyasova
5- Howard
Orlando Magic:
4- A Gordon
5- Vucevic
Los Angeles Lakers:
4- Randle
5- Zubac
Los Angeles Clippers:
4- Griffin
5- Jordan
Sacramento Kings:
4- Cauley-Stein / Labissiere
5- Koufos
Phoenix Suns:
4- Chriss / Bender
5- Len / Chandler
Golden State Warriors:
4- D Green
5-
Portland Trailblazers:
4-
5- Nurkic
Denver Nuggets:
4- Jokic
5- Plumlee / Faried
Utah Jazz:
4- Favors
5- Gobert
Memphis Grizzlies:
4-
5- M Gasol
Minnesota Twolves:
4- Dieng
5- Towns
OKC Thunder:
4- Gibson
5- Adams
Dallas Mavs:
4-
5- Noel
San Antonio Spurs:
4- Aldridge
5- P Gasol / Dedmon
Houston Rockets
New Orleans Pelicans:
4- A Davis
5- Cousins