Isaiah Thomas, Avery Bradley, Marcus Smart, & Al Horford.
Thomas might be small but he packs a huge punch. An offensive star in his own right could get his in a multitude of ways inside and out. He and his teammates can create some magic like this.
Any defensive issues he could run into can be mitigated with the latter three on the team, where Bradley and Horford can also provide plenty on offense to ease the load.
The one area that comes to mind on how the Suns can get the better of the Celtics is the rebounding department.
The Celtics aren’t a good rebounding team but the Suns are! If they can capitalize on the boards and Booker can continue to give them nightmares, then they should have a good shot to win. The key here would be Williams vs Horford as it relates to the battle of the boards.
On a good day though, the good touch on offense combined with a very solid defensive front would get the better of the Suns.