Joyce is painfully slow - but he has a Bruno-like jab, a granit chin (at least that's how it seems so far) and great endurance. His controlled, relentless pressure will probably be too much for most top boxers to handle. In a 12-rounder, I see him walking down Grant before the half-way stage.
Joyce is the more talented fighter. But Grant is underrated. Back in the 90s he took on and beat a long list of high risk-low reward men. While his skills were pedestrian, he was big, strong, hard hitting and at times showed heart and guts. This is a toss up.
It's funny because Grant actually has a better resume. I think Joyce is significantly more skilled but Grant is definitely better than Dubois