Put it this way:
Bruins owe the Leafs a 2nd pairing D for the Kaberle trade back in 2011. This is it.
Leafs got a 1st, 2nd, and failed 1st round prospect Colborne.
Kaberle was a rental. Carlo would solidify the top four perfectly and push the Leafs to the ECF.
1st, 2nd, failing 1st round prospect (Max Domi is a former 1st rounder).