The former All Blacks and Kiwis representative makes his return to rugby league next month after last playing the sport in 2014.
Williams has played at three Rugby World Cup tournaments and the 2013 Rugby League World Cup.
Reports out of Australia had previously said the 34-year-old was considering playing for Samoa at next year's Rugby League World Cup.
"I haven't proven myself in Super League yet," Williams told media on Wednesday.
"I've been away for five years and for me to start thinking about playing for New Zealand or Samoa is ridiculous.
"I'm here, and I'm fully focused on being with the Toronto boys to see if I can play the 13-man game.
"I always have a point to prove, no matter where I am. I wouldn't still be around after 18 or 19 years if I didn't have that inner drive to succeed."
Williams said he's aware a main part of his role in Toronto is to help spread rugby league's popularity in North America and he's fully behind it.
"I understand that the responsibility is to use my profile in whatever capacity I can to help grow the game – and I'm all for it," he said.
"If it means doing a bit more of this stuff, or going and speaking to young kids, I'm for it.
"This is such a blessed opportunity, being able to experience this on and off the field. If it opens a few doors for kids in Australia, New Zealand and the islands to succeed … how cool would that be?"
