Phoenix and NY seem like obvious names, but I'll add Philly.
Westbrook and Gordon for Harris and Horford. Other minor pieces and draft picks could be included. I think that would be an interesting trade for both teams. And sure I don't think Westbrook is the best fit with Embiid and Simmons, but I do like Gordon on that team and it isn't like Harris and Horford work either. Sixers starting 5 would be immensely talented with Westbrook, Gordon, Richardson, Simmons, and Embiid so they might try something like that. For Houston, I think Harris would actually work well as Harden's #2 guy and they definitely need some size, and while Horford struggled last year, I think he would be more effective in Houston's system as the starting center than he was a starting PF and backup C in Philly.