Wellington - All Blacks star Sonny Bill Williams is reportedly weighing up a bold offer from Canada's Toronto Wolfpack that would make him the highest paid player in both rugby league and rugby union.

Williams, 34, is expected to call time on his union career after the Rugby World Cup, which will end in disappointing fashion for the All Blacks on Friday with a third-place play-off against Wales.

The Wolfpack, who won promotion to England's Super League this month, is prepared to pay Williams Aus$9.0 million ($6.2 million) over two years, the Sydney Morning Herald reported.

It said several rugby clubs were also chasing his signature but could not match the Wolfpack's offer, which it described as a record for both codes.

Citing unnamed sources, the newspaper said the bidding war was set to prove too rich for clubs in Australia's NRL, where Williams began his remarkable sporting career.

The Wolfpack have made no secret of their desire to recruit one of rugby's most recognisable players and have the funds to do it thanks to mining-magnate owner David Argyle.

Australian-born Argyle said earlier this year that Williams "is box office and puts bums on seats".

"He is rugby's LeBron James and we see his recruitment as bigger than when David Beckham joined LA Galaxy," he told Fox Sports Australia in February.

While based in Canada, the ocean-hopping Wolfpack compete in England and Argyle's ambition is to give them a global profile.

Williams was non-committal this week when asked about his future in the wake of New Zealand's World Cup semi-final mauling at the hands of England.

"Soon bro, soon, we're just trying to finalise that," he told reporters.

Williams has won two World Cups in his 57-Tests with the All Blacks, as well as numerous Bledisloe Cups and Rugby Championships.

Other honours include a Super Rugby title and two NRL premierships.

He also triumphed in all seven of his professional heavyweight boxing bouts, winning the New Zealand title in 2012.

Williams suffered a string of injuries this year and hinted it could be his last season playing rugby union in New Zealand.