In a chat with The Times, Santa Cruz (31-0-1, 17 KOs) confirmed that he and Mares (31-1-1, 15 KOs) had a verbal agreement about the bout.
"I can't wait. It's the fight everyone has wanted for me," Santa Cruz told The Times.
The 29-year-old Mares, who has held the IBF Bantamweight, WBC Super Bantamweight and WBC Featherweight championships, will be a very tough test for Santa Cruz having only ever lost one fight.
The 26-year old, Santa Cruz is known for his great body punching and this bout has the makings of being a classic.