United boss Sir Alex Ferguson had Bonucci watched last season when he was with Bari.
The young defender revealed: "Juve are the top. I know that in January, Man City came looking for me, and more recently Man United. But when the offer arrived from the Bianconeri, I had no doubts.
"I will grow even more here and in 2012 I see myself together with Chiellini, Ranocchia and Bocchetti in forming the group of centre-backs at the next European Championship."