Either Muslims or Alien Space Bats.
Well I know the Catholic European Christians there were called "Franks" but that's what every Catholic European Christian was called by those outside Christendom at the time, so were they actually French?
It's pretty vague according to Wikipedia. They were probably a mish-mash from every group in Europe.
I'm guessing they'd end up speaking a Romance language, what with all the Latin?
My guess is - depending on how tumultuous the centuries are in the Holy Land, and the Mongols, Mamelukes, etc in surrounding regions - more European immigrants, particularly Italians, Greeks, French, possibly even a flow of Germans. Still, I can't see them being more than 20% of the population in any TL. There will always be a far greater percentage of the locals. Maybe a sort of mestizo mixture (or whatever word is used) between Europeans and Arabs.
Just my guess.
Fun fact: there are traces of the Crusader's and Italians who set up shoppe in the Levant today. I was taking with the wife of a restaurant-owner, who is Lebanese, who said that I could easily pass as Lebanese. My Mother, in her wisdom, decided to point out "But he's too pale!". The owner's wife replied that it's completely unheard of to see blonde people in Lebanon (it might have just been where she was from) because the Crusaders, Venetians, and Genoese all intermingled with the residents of the Levant, I guess.
Take this for a grain of salt but the Western population in the Kingdom of Jerusalem was bordering on 25%.
How many of those were soldiery? That is, how many were crusaders only there temporarily? Just wondering.
I'm sure over the centuries the place could become majority Christian, or at least plurality. Maybe not during the time of the Crusades, but later with immigration and demographics. Israel managed to do it, the Crusader States can do the same thing with centuries of time. Not a savory or fortunate scenario, but a realistic one, I think.