Bob McKenzie described what he thinks the Leafs are looking for a few days ago:
“I do think the Leafs are looking, but I think it is a very specific need. I think it is a right-shot D or a left-shot who has a lot of experience of playing on the right side, and it is also somebody who has a significant amount of term on his contract — and by significant, I would probably say the low end of the bar would be what they did with Muzzin.”
The cost would be significant — most likely Andreas Johnsson or Kasperi Kapanen, or possibly Kerfoot, as Bob McKenzie mentioned (though I personally doubt a Kerfoot trade is likely given the importance of the 3C position on the Leafs).