Newton is out of contract at the end of the season and is reportedly on the radar of Wakefield Wildcats after stating his intention to leave the Bulls.
L’Estrange, meanwhile, has signed a two-year deal with the club meaning he will stay in Super League until the end of the 2011 season.
Coach Steve McNamara said: “Heath’s a quality hooker and a quality person.
“Obviously, he’s a replacement for Terry Newton and I’m excited by what he can provide for us when he gets over here.
“He’s another Grand Final winner and he’s still only 24 so he’s at the perfect age and I’m excited about him coming to the Bulls.
“I think Heath and Wayne Godwin will complement each other really well and I think he’ll be very good for us on and off the field.”
L’Estrange will join his teammate Glenn Hall at the Bulls next season and added: “Bradford’s a great club and I can’t wait to get there. Both myself and Glenn Hall have talked about it and we both feel the same.
“I liked Bradford when I was younger and thought – while I’m still young – I want to take this opportunity while I’ve got it. Hopefully, we can help get the winning culture back there.
“Now I want to get over there and rip in to Super League,” he said.