Oh I give up... A source says Britney Spears' ex, 30, may be heading to NYC in September to make his Broadway debut in Legally Blonde, the Tony-nominated musical adaptation of the hit film, Us Weekly reports in its latest issue, on newsstands now.

"He's so excited!" a Federline source tells Us.

The former backup dancer and aspiring hip-hop artist -- who is hitting the gym after packing on "daddy weight," ex Shar Jackson says -- will test his song-and-dance chops in a trio of roles -- including the UPS guy who inspires the "bend and snap."

"This is his chance to show the world what he can do," says a pal.