From Emily Cahn, politics reporter at Roll Call:

Virginia has a sore loser law, so that means he cannot come back to run as an independent or write-in in #VA07 — Emily Cahn (@CahnEmily) June 11, 2014

Correction: A reader pointed out Cantor might be able to run as a write-in, since the Virginia law only explicitly forbids his name from appearing on the ballot.