That's Troy Baker and Ashley Johnson
The Last of Us came, it went, and it conquered. The game reached pretty much universal acclaim (myself included) from around the web, and now, if you're curious, you can see what went into the roles of Joel and Ellie from a Q&A session featuring Troy Baker and Ashley Johnson. I challenge you to stop staring at Troy Baker's perfect hair.
If you've ever wanted to know what goes into voice acting, this is a great video to watch. Naughty Dog really does an excellent job of giving us behind the scenes looks at how the industry works, particularly regarding Uncharted's excellent motion capture extra videos.