Walesonline.co.uk has reported that So'oialo, 33, has been in discussions with both the Cardiff Blues and Llanelli Scarlets to move from his Suzuka-based Honda Heat base where he has played for the past two seasons.
So'oialo, a 2002 Commonwealth Games Sevens gold medalist played in the New Zealand 2003 and 2007 Rugby World Cup campaigns. He moved to Japan after missing the 2011 Super Rugby season as the result of injury.
The Welsh website said a transfer to Wales looked likely so long as terms could be aagreed and So'oialo was able to prove his fitness.
The Cardiff franchise have room for an overseas players and had been looking for a replreament for another New Zealander, Michael Paterson, who is playing for Sale this year.
If So'oialo was picked up by Wales he would be partnered in the loose by Lions captain Sam Warburton and South African Andries Pretorius.
The option for the Scarlets would also suit as their captain Rob McCusker, who played No.8, prefers the blindside of the scrum which was vacant after Ben Morgan transferred to Gloucester. The back-up No.8 for the franchise Keiran Murphy moved to Brive.