My position is that they should only trade Brown if it is a really good trade for the Celtics, full stop. So all my proposed trades are going to be good for the Celtics.
Atlanta seems like a viable trade partner. My Atlanta trade is as follows:
Brown
Muscala
for
Murray
Bey
Okongwu
This does not fully address our roster imbalance as the key piece coming back (Murray) is another combo guard, but we get a solid back up wing (Bey) and a young big, so overall, I am OK with this. Smart or White may need to go in a subsequent trade to address roster balance.
I think another potential trade partner is Toronto:
Brown
White
for
Siakam
Barnes
Achiuwa
I am not thrilled to give up White (I think many would prefer to send out Smart and that is fine, it still works) but we add a lot of versatility and get bigger. I think both Siakam and Barnes would do well with Tatum. I know that TOR including Barnes is a stretch but if they want Brown, they are going to have to give something up.
The final trade I have thought of is a straight up Brown for Towns. Towns has the same contract issues later that Brown would have, we end up with two really big contracts. Towns is a risk, he has had some inconsistency, but I think if you got him on the right team, he would be the star that he has shown flashes of being (more than flashes really).
The Brown for Murray stuff just puzzles me at this point. Brown is waaaay better than Murray, we just saw him kick his butt all over the basketball court for 6 games. Jaylen Brown held Murray to 3-16 shooting when guarding him, Jaylen Brown put up 11-18 shooting when being guarded by him. Look, I know we have short memories as fans but this was like 4 weeks ago.
As for Brown/Siakam, that isn't happening. The Raptors are not, literally 0% chnace, trading Barnes and Siakam for one season of Jaylen Brown. And that's what it would be, since trading both Siakam and Barnes means the resulting team probably isn't good enough to get Jaylen to stay. They refused to trade Barnes for 4 years of KD last off season, they aren't moving him now.
Even straight Brown for Siakam probably isn't happening. That swap maybe makes the Raptors a little better, but good enough to get Brown to re-sign? Ehhhhh, probably not. Meanwhile Siakam has the same problem Brown has, he's an expiring. The difference is Boston has the "hammer" of a super-max offer they can use on Brown, they don't have that for Siakam, so he's a MUCH bigger flight risk. And older.
A five year deal for Brown is his ages 28-32, for Siakam its 30-34. That matters a little as well.