Brendan Donovan or Alec Burleson in left field, Lars Nootbaar in center field, and Jordan Walker in right field
This scenario leads to their strongest offense, but probably their weakest defensive alignment.
Nootbaar is a quality center fielder, but he's not the elite defender in center that can raise the overall defense that the Cardinals may need. If the Cardinals really do add a lot of strikeout stuff to their rotation and bullpen in the near future, they may be able to afford a lesser defense that allows them to prop up their offense even more. Just look at the kind of lineup they could run out.
1. CF Lars Nootbaar
2. 1B Paul Goldschmidt
3. 2B Nolan Gorman
4. 3B Nolan Arenado
5. C Willson Contreras
6. LF Brendan Donovan
7. RF Jordan Walker
8. DH Alec Burleson
9. SS Masyn Winn
There's an arguement to be had that the defense will improve next year even without an upgrade in center field. Walker has been showing signs of improvement in right field lately, and if he can be even league average next year, that's a huge improvement. Another year of Contreras behind the plate could calm down some of the issues he has had. Gorman continues to improve at second base, and Arenado is back to looking like himself at third. This isn't even to mention a full season of Winn at shortstop.
Assuming one or two of Edman, Carlson, or O'Neill are still with the team next year, they'll still have defensive options to lean on throughout the year as needed. The Cardinals' strength is their lineup, so doubling down on that makes a lot of sense.