If I play MP solo, do I get more xp?

Everyone gets the same amount, you don't get more from doing it solo.

Actually you get much less doing it solo.
It is as Bateman said, the total xp collected is awarded to all team members.
However due to the scoring mechanism of MP a team will collect way more XP clearing the same 10 waves of enemies than a solo player does, this is due to the various bonuses for weapon use, power use, power combos, headshots, grabs, streaks, wounds, etc.
4 team plat game can easily score in the range of 700k XP, while most plat solos score 300k-ish.