Source? Can't find it right now but I'm 99% sure I saw something about them having a deal in place for McDonagh, and then Gorton throwing Miller into it too.
From a couple mins of searching I found this, which suggests they were not looking to re-sign Miller.
Q: How did it come about that you had to include Miller?
A: Number of discussions with Stevie y, had decisions to make with JT. We were comfortble with what we were getting back.
"Namestnikov is a player that we have liked for a while. It hit on a lot of things that we wanted to do as we move forward is probably the best answer."
I think you're both partially correct.
Yzerman had asked in the past about Miller, and had him on his radar for a while.
With this particular trade, it was Gorton who brought up Miller to Yzerman as the deal took shape.
My guess is that both GMs saw something they liked in the players they received, prior to the trade.
As for who asked for whom, it probably depends on how you want to view it. Yzerman with the initial inquiry (or inquiries), Gorton remembering it and initializing in this particular conversation.
Either way, I think both teams focused on a player they had on their radar for a while.