I haven't started the civil war at all yet, and i plan on siding with the imperials after tha main quest.

What options should i choose at the meeting?

Can you possibly be any more vague?
Which "meeting" ?

To join the Legion, go to Solitude and speak with Legate Rikke.
But it makes no difference what you say to anyone, at anytime... apart from when you agree to join the Imperial or Stormcloaks. Just choose one side, and then follow the quests.
Once you start the quests, everything else just happens along a fixed path.