Cardinals receive: RHP Bryan Woo
Mariners receive: 2B Nolan Gorman
Since I feel like Gilbert may end up being a hard guy for both teams to agree on when it comes to proper trade value, I think Bryan Woo is a name that could come up for both sides.
In 7 MLB starts, Woo is 1-1 with a 3.63 ERA and 43 SO in 34.2 innings pitched. Woo is a top-100 prospect in all of baseball and would be an excellent get for the Cardinals rotation, but he'll come at a high price.
I almost had this swap being Tommy Edman, but with his injury and struggles at the plate this year, I think the Mariners will pass on giving up one of their best young arms for Edman. Perhaps a prospect like Emerson Hancock would work, but I really do think Nolan Gorman makes a ton of sense for Seattle.
Giving up Gorman would hurt a lot, but it's going to have to hurt to get a young arm like Woo or Gilbert. Gorman could come back to bite St. Louis, but I think they'd rather chance that than give up Jordan Walker, Lars Nootbaar, or Brendan Donovan.