The cashed-up Top 14 outfit has outlayed 450,000 Euros to ensure Mason follows in the footsteps of his former Canterbury-Bankstown teammate Sonny Bill Williams.
It's likely he, like Williams, will play inside centre, switching from a rugby league forward to a powerful rugby back.
Mason visited Toulon last Wednesday with his London-based manager Greg Keenan.
According to French reports he was "seen having coffee with [Toulon president] Mourad Boudjellal".
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Boudjellal is the eccentric comic book publisher who owns Toulon and signs the biggest cheques in world rugby to recruit the best players.
Giteau recently signed a $900,000-a-year contract to join Toulon's galaxy of stars.
English Test star Jonny Wilkinson is already playing for Toulon, and Springboks hardman Bakkies Botha will join the side next year.
There's also speculation that Williams will return to Toulon, and once again will play alongside his former Bulldogs teammate.
Toulon recently offered the All Black a staggering $1.8 million per season to return to the south of France after the Rugby World Cup.
Williams joined Toulon after fleeing his Bulldogs contract in 2008, and played for two seasons before returning to New Zealand last year.
In dominant form for the Crusaders, Williams has been among the best players in the Super Rugby competition and his former French employer is keen to re-sign him.
But the signing of Mason as a centre could also be Toulon's back-up option.
Mason is not in the same class of athlete as SBW but Toulon may be keen to see if they could transfer his 118kg size and handling ability into a line-breaking role at centre.
Mason also holds a Tongan passport, which would mean he does not qualify as a foreign import for Toulon.
Mason has considered a code switch before, having spoken with then New South Wales Waratahs coach Ewen McKenzie about joining the team in 2007.
He also visited Japan in 2009 to talk with rugby clubs.
The former Kangaroo recently joined English Super League club Hull on a three-year contract.
