Buyer or seller?
Neither, really. Management insists they are not in the rental market one way or another, but they want to make a "hockey deal" that can add a player for next season and beyond. It's not impossible they ship out one of their pending free agents, however. Toronto is in a bit of a grey area: They're in solid playoff position so they're not about to tear things down, but they also don't want to give up futures for players who won't be with the organization long term. The Leafs are going to be listening to everything in the next few days, but it's possible they don't make a move at all.
Toronto's biggest hole is a longstanding one: They have to get better defensively, and that starts on the blueline. Adding an elite defenceman that can play in the top four and on the right side is priority No. 1, but the Leafs are also interested in adding up front given they could lose four of their top 10 forwards to unrestricted free agency in the summer. Landing that kind of blueliner isn't easy but there are some intriguing options out there, albeit mainly ones that play the left side (Alex Edler and Christian Ehrhoff come to mind).
On the block
Nikolai Kulemin, James Reimer, Mason Raymond, Nazem Kadri, Jake Gardiner, Dave Bolland
The Leafs are exceptionally tight against the cap once Bolland comes off of injured reserve and will likely have to move an equal salary out to bring salary in. That complicates things considerably and is yet another reason they may have to wait for the off-season to make more moves.