I think Giffey would be our best bet against Doug. Kromah might be the best perimeter defender on the team, but as caw said, McDermott can be lethal in the post and Giffey has actually been pretty effective down there. Of course, Doug is a whole other animal than anything Giffey has seen, but he's probably the most versatile defender on the team.
But whoever drew the initial assignment is probably only part of the story. McDermott would probably see a lot of double teams, especially in the post. Ollie loves to have Boatright and Napier double down against dangerous big men because of their uncanny ability to cleanly strip them off the dribble. It's possible that McDermott would make us pay by passing out of the double team (I'm sure he's not unfamiliar with double teams at this point in his career), but I'm pretty confident in Ollie's ability to at least give him different things to think about.