Emperor Constantine said:
Then he might as well marry one of Napoleon's sisters. That would technically be the best bet.
Marc Pasquin said:
Some might see this as bringing together both of France's monarchial's houses while some royalists might have an issue with him marrying the sister of "The Usurper". Could go both ways really.
In my opinion, the opinion of the royalists doesn't matter much: it's Napoleon who would have the cards in hands. If he wants to marry Louis XVII to one of his sister, he will do it and there will be no opposition.
The main problem would come from the timing. Of Napoleon's three sisters, Elisa is most likely ruled out: she married Felix Bacciochi in 1797 and they remained married until her death in 1820.
Pauline Bonaparte is a more likely case. She was first married in 1797 but her husband, Charles Leclerc, died in 1802. She remarried to Camille Borghese in 1803 but Napoleon could consider her as a brider for Louis XVII if he choose to restore the monarchy. To further this idea is the fact that Napoleon and Pauline were extremly close: so the idea of making his beloved sister Queen of France would be a wonderful gift for Napoleon. Louis XVII would also be 17 in 1802, so he would be in age to marry Pauline if he already isn't by that point.
Then there is Caroline. She married Murat after Brumaire, but on January 1800 so a few months after the coup. That makes her technically available for Louis XVII, but I'm not sure the idea of restoring the monarchy and the idea of marrying one of his sister to Louis XVII would come to Napoleon such a short time after his coup.
There is another person Napoleon could choose to marry to Louis XVII of course: his stepdaughter, Hortense de Beauharnais. Napoleon always cherished the children of Joséphine, so having Hortence marrying Louis XVII could be an interesting choice. And Hortense didn't marry Louis Bonaparte before 1802.
That being said, all of this still depends on Napoleon's personna and on what he decides to do with Louis XVII.