When this happened to me (and I've done a lot of Crusades in my game, so happened a lot) I used the character finder, selected my culture, my religion and ruler no sorted by Stewardship and started to grant them lands. Check their traits the worsted are Ambitious and Envious, the other the more reddish one don't count for you.
I've adopted this strategy I do choose the character you wanted and:
1. Do you want to make him a feudal lord? Grand him a barony.
2. Do you want to make him a prince-bishop? Grand him a bishorship.
3. Do you want to make him a mayor? Grand him a city.
Then I filled the other slots of the county, then I've gone in the other counties of that Duky and repeated, I personally hate to see them fight between them so I give all the Counties of a Duky to only one and I make him Duke... at second of what first title you've given first to him you'd obtain a Duke, a Prince - Arch Bishop or a Doge in this way.
The only times I don't do this is if I've a courtier with a weak claim I could press in this case I give him only a Barony no more as he'll get land after, so he don't become too powerful.
If you become an Emperor after you could grant the Kingdom of France to the best vassal, better if he is of your dynasty so he'll add score, but it is better France is fractured before doing this maybe making more bigger Aquitania, Burgundy and Brittany of that they was: united Kingdom of France in my game did 111 K soldiers! A pain in the a**s when they revolted!
... or maybe in better to retain France as one of your title, I regrets to have not done this in my game.