"Manu is an exciting player. He is the right ambassador for us at the right time," Mr Evans said.
During the tournament, shortly after both brothers were hit with the fines, Opro managing director Anthony Lovat hit back at claims they were involved in ambush marketing.
"Opro is a professional organisation and has never and would never be involved in ambush marketing activities," Dr Lovat said last month.
The company had also offered to pay the brothers' fines, but both had already been settled - with older brother Alesana's fine paid with the help of members of the New Zealand and Samoan communities and a sausage sizzle fundraiser.
After he was fined, Manu Tuilagi continued to wear the unapproved shield, having covered the Opro logo by colouring over it with black marker pen.
On being named the new face of Opro, Tuilagi told British media he had always worn its mouthguards as he felt they were the best fit.
"My Opro mouthguard is the most comfortable one I have ever worn," he said.
"To be the best, I have to wear the best."
Tuilagi also made headlines at the business end of the Rugby World Cup when he dangerously jumped off a ferry about to berth on the Auckland waterfront.
He was met by police and later fined by his coach.
The incident followed a boozy night out after the English team's quarter-final loss to eventual cup finalists France.
