1st October 2017, 20:39 | championship
The former Castleford Tigers and Hull FC player has joined the newly promoted Kingstone Press Championship side on a three-year deal, after Warrington Wolves accepted an offer of £130,000 from the Canadian side.
Westerman told the Wolfpack's official website: "I was attracted to the club because of what I'm seeing and hearing off players who are already there.
"It's a massive club with great support and I think it's only going to get better and bigger. I want to be part of a side that gets the club into Super League where I think it belongs.
"I'm looking forward to getting started and playing in front of the Wolfpack crowd."
Toronto director of rugby Brian Noble added: "With almost 300 games under Joe's belt already at the highest levels of the game, this is a real coup for the Wolfpack with Joe's best years still in front of him."
Toronto have also signed London Broncos hooker Andy Ackers on a two-year deal.