Charles and Hopkins match up fine for size. Charles is the only man of Hopkins's size I would pick to get him out of there.
Bernard was not a great 175 pounder. Ez was. Bhop stands no chance at 175 but might last the distance.
I think Charles would be the hardest, smartest and most powerful fighter he would have faced, I don't think he gets away with a spoiler contest, he might last it out, though I think he'd meet with a tko or ko. Bhop to me, is one of Boxing's 'jammy' champions, in a purist's world he might not see the title. as always, who knows. But not with Charles is he having fun.
Ezzard Charles might be the P4P best of all time, Charles has already beaten guys a lot better then Hopkins, Charles turns him and basically any 175lber since the 90s onwards into a punching bag.
I'm going for Charles by decision after a close fight. Hopkins's ability to control the distance, his obstructive style and his ring IQ would have made life difficult for any of the best middleweight and light heavyweight boxers of all time. But Charles was a true phenomenon and would have beaten the Executioner, even if he suffered.