The problem with that route is two-fold as I see it.
1. There aren't many/any pitchers available at the caliber of Rodon, Verlander, DeGrom, etc on the trade market. If the Brewers sell, maybe Woodruff?
2. The necessity of giving up multiple top prospects who will soon be cheap, cost-controlled contributors at the MLB level in order to trade for even a #2-3 pitcher. Just think about what the Twins would have to give up to get, say Sandy Alcantara. Would you give up Lewis, Brooks Lee, Miranda, Larnach, Bailey Ober and Austin Martin/Jorge Polanco for Alcantara? I don't even think the Marlins would do that.
I'd rather sign Correa and Rodon. They just cost money. If Lewis and Lee turn out to be stars, great. You can trade them to fill other needs if you can't find them MLB at bats.