Will Half Life 2 Episode 3 be on the Xbox 360?

In short, yes it can (if you mean Half-Life 2. The original Half-Life was not released on the Xbox). You'd be better off though if you got a copy of Orange Box for the 360. I has HL 2, its two expansions, Team Fortress 2, and Portal. All on one disk. It currently sells for $20 new, but can be had for cheaper used.