I don't want Siakam, he's too old and a poor fit with Grant. In general I've been a proponent of using the #3 and not trading for a veteran to win with Dame.
Bridges and Brown are the two targets I would consider Ant and #3 though. Bridges is younger at 24, an iron man, and on a cheaper contract. Brown is the superior All NBA player. Brown is only 26.
There is certainly a lot of risk with this move.
#3 could ultimately be a superior player
#3 is on a cheaper contract
#3 is younger
#3 allows the Blazers to additionally have Ant salary plus another player under the luxury tax vs Brown supermax
Ant still has upside so the Blazers likely aren't selling at the peak of his value
Brown has injury concerns
Ultimately I probably pull the trigger on this deal as a few more veteran role players, Sharpe improving, good Blazers health, other contenders not having perfect seasons, all of that might give the Blazers a longshot chance to contend. It's still unlikely the Blazers win a title, but it's probably worth taking that shot.
Things I like about this move;
Break up the DameAnt duo which isn't good enough defensively
Brown is a great wing defender that is a two way 20+ppg scorer.
Brown can defend SG or SF, especially SF when paired with a tall SG such as Sharpe.
Brown is a great frontcourt fit with Grant, allowing Grant to roam defensively while Brown locks up the #1 scorer.
Brown is close with Dame so I'd view his flight risk in free agency to be very low just like Grant.
Blazers aren't mortgaging their future draft equity if they need to eventually rebuild around Sharpe or even do another final trade for a 3rd all-star.
Brown is likely to have a lot of value in a few years if this group is unsuccessful and the Blazers are better off rebuilding around Sharpe
So I believe I pull the trigger on this trade
I'd expect Ant to do awesome in Boston, probably top10 or even top5 in the league in scoring next year, and have some eventually question if Portland traded the wrong PG.
Does Boston pull the trigger? If they want additional assets I'd probably walk away and tell Dame Brown they need to pressure the Celtics as was done in the Grant trade.