Really comes down to if Joyce can take his power. Tua no doubt can crack but Ike took his best shots and Joyce has always been more susceptible to getting caught with right hands due to his busy jab rather than left hooks. I suspect Joyce with his size, durability and work rate would win a decision in a 12 round war. His jab will score all night, subduing Tua for long periods and Joyce's work rate ensure he wins on the cards.
Joyce's chin is being overrated after facing Paint Dry Pudding Parker and One-Eyed Daniel Dubois who couldn't land a clean right hand.
This as I said a bit different than taking punches off those guys, and taking punches off a top 10 hardest hitting Heavyweight of all time, who's power is dangerous from round 1 to 12.