Sen no Kiseki 3 does not have any means to import bonding choices from the first two games. So because of this the dialogue and options will not change. Regarding your options you still can go for anyone you want but the scenes are distinct enough that some people are favoured a lot more romantically. There is only one person that kisses Rean for example.
I am shocked in the third edition of Trails of Cold Steel that there is actual student trying to seduce him because there is nothing wrong with that because he is much closer to age to the students than the teachers from Thor Academy were.