Per BTV, Alcantara (2 yrs $38mill) has a surplus value of $10.1mill. From Boston, an equivalent package could include any one of Perales, Early, Valera, Romero, Cespedes, or Dobbins. No idea how Miami feels about any of them. Some might be worth the risk for Alcantara. Probably not Early or Dobbins. You might need one or both if you trade for Alcantara.
With a contract worth $38mill over 2 years and a surplus value of $10mill, projections have Alcantara at 6 fWAR over 2 years or 3 fWAR per year. I think the Sox could get that from either Early or Dobbins instead.