How about something like:
CBJ receives:
JT Miller (extended)
VAN receives:
Kirill Marchenko
rights to RFA Adam Boqvist
2023 1st round pick
From CBJ's perspective, they can leverage their surplus of good prospects, and acquire that elusive 1C without giving up their best young assets (Johnson, Sillinger, and their two 1st round picks this year). The injection of guys like Miller and Johnson into their line up may mean the 2023 first ends up being in the latter half of the round.
From VAN's perspective, this fits the player/prospect/pick mold that they are rumored to be looking for. It also addresses some organizational needs by netting them a young RD and a potential top six prospect. Columbus is in the deepest division in hockey, so the chances of the 2023 pick being a premium one are also decent.
JT may agree to the extension as he is coming off what is likely a career year, and cashing in now seems like a better bet than risking injury or a down year. Columbus has the cap space to sign Miller, and he is from Ohio as you mentioned. Unlike other teams rumored to be interested in Miller, CBJ can also give Miller the opportunity to be a bonafide 1C while playing with great wingers.