First off, why the teams would not do this trade:
Miami: After trading for Powell, i'd assume that they would want to resign him, and that becomes a lot harder after trading away the expiring salary of Terry Rozier. Additionally, Jamie is a decently good, youngish player, even if he has beef with Spo (from my understanding) and doesn't get played much anymore. 4 seconds is all the remaining second round draft capital Miami has, hindering their future ability to make small trades. Holiday was not very good last year, so they also might not want to take on his big contract.
Portland: keeping Holiday allows them to throw out a defensive menace line up of holiday, thybull, Deni, Camara, and Clingan that would shut down teams for long stretches. They might want more draft capital and/or a more intriguing young player than Jaquez Jr. Portland also uses a great mentor for scoot/shaedon and anchor of their defense.
Why the teams would do this trade: -Miami: Miami shows their fan base that they are willing to make moves to build out this team in the extremely weak East. They find a great point of attack defender to put in the backcourt who can also mentor Mitchell. They bring championship experience to the team, and I personally think that he would be a great fit next to Herro/Powell. With this move, Miami's defense would be extremely formidable, especially in the East. I think that this move in addition to aquiring Powell, gives them a chance to fight for a solid playoff spot.
-Portland: They get back greater returns for Simons and get back 4 seconds (as well as their own they got back due to Jrue performing poorly on his physical), as well as expiring salary in Rozier and a young bench player in Jaquez to bring more depth to the roster. Reports state that Jrue is very unhappy about being traded to portland so Portland grants his wish and moves him far far away from dreary Oregon. Portland would aquire more picks and continue to bide their time in a hellish gauntlet of the current Western Conference. Making a move too soon (which i think is right now) would doom them to another bout of mediocrity among the juggernots of OKC, Denver, Spurs, Mavs, and also to a lesser extent TWolves, lakers, clippers.
Final Thoughts: I think Portland is more likely to say no. From my understanding they like Jrue and i think that: 1: Portland asks for more than this package, and if im Miami idk how I would feel if i was being asked to give a FRP for Jrue. 2: Portland traded for Jrue, and I'm assuming they want him to help guide their young team to become a competent defensive backcourt. I wouldn't be shocked if Miami said no. IDK the exact value on Jrue, and I feel like both Fanspo communities will have something to say about this trade.