Planning on applying here- how hard is it to get in undecided?

I really want to go here, and I'm undecided. I have average grades for here, and very little extracurriculars. Do I have better chances applying as undecided, or choosing a major that I may not want but I'm interested in?

My thoughts for a major I would choose just to apply as would be something like Actuarial Science (in Business school), Computer Science or something in Letters and Sciences. If it's better to have a major selected, which of these schools would be easiest to initially get into? I've heard CS is a harder to get into.