Small fixes

Boston not trading a 2nd for Miller.

I am sure you are correct.
I would actually hope Buffalo would sign him before the TDL for at least 3 more years (before their prospects ELC expire).
But IMO Toronto would be a better target as they only have Holl and Liljegren who shoot right and they only have one point between the two of them.
Also, among all Leaf D-men, only Reilly has more goals and assists than Miller.
If the Dubas was confident the Leafs could get to the final four, maybe Karmanos could extract more than a 2nd out of Toronto.

Why would we resign Miller?

Who do the Sabres have to play RHD next year? Jokiharju then...
Miller is playing well and only Dahlin has more goals and pts.
He can PK and PP while only Dahlin has a higher TOI/GM than he.

A very optimistic alternative:
Management thinks Oskari Laaksonen is NHL ready and Dubas want Miller and thinks the Leafs will get to the final four and would give up a first round pick for him+.
But looking at this team and next years team he is worth more than a late 2nd to the Sabres.

I'd much rather find some vets in FA & trade miller for a 2nd instead of signing Miller to a 3 year deal. We signed Pysyk in FA for cheap and has been playing well.

Miller isn't really playing well. He's a bit careless with the puck. Takes a lot of low quality shots that kill possessions. He's had some terrible mistakes that cost us the game like the Leafs game.

He's got points, but that's not a good way of evaluating a d man. Risto had a lot of points too.

Laaksonen would probably be up next year I'd assume. He'll be 23 with 1.5 Rochester seasons under his belt already. He can obviously play the PP too. Could just roll out Joki, Vet signing, Laaksonen.