I agree that Simmons is not a realistic target unless we include Fox or Haliburton. He's a 25 year old 3-time All-Star with 4 more years on his contract. He's only being talked about as available because of special circumstances and Morey seems to be upping his asking cost as the relationship gets more strained which is... interesting. I do think he gets traded eventually but someone else will beat our best offer. Probably Portland or Golden State.
I really don't know what Siakam's value is right now though. He's in that weird category of players who are obviously overpaid because they're not quite franchise players but they were too good to let leave in free agency. It really just comes down to what the Toronto front office's plan is. If they still consider Siakam as part of their core there's no reason to trade him unless they get a huge offer. If they're looking to go in a different direction and get younger, acquire picks, clear out cap space, etc. they can certainly ask for Haliburton or any other emerging star on a rookie contract but they don't have leverage so they'll ultimately have to settle for less than that or figure out a way to keep all of their forwards happy with their roles.