I'm certified in both. Don't think there is any built tool for it to my knowledge at least. Guess it's the standard issues. Items in Sitecore roughly translates to pages in Episerver. Components maps to blocks etc. I would probably build an export tool in Sitecore that uses the Episerver new REST api to push in content. Most functionally needs to be ported / rebuilt but some integrations can probably be reused if it was built with decent architecture.

I'd want to add that you can "extract" data from Sitecore using its Content Service. Read more about it here:

http://www.sitecore.net/learn/blogs/technical-blogs/john-west-sitecore-blog/posts/2013/09/getting-data-out-of-the-sitecore-aspnet-cms.aspx

Yup...so depends in what solution you would rather be programming. If you have the source of both then both ways are pretty equal. Still take quite a bit of coding though to migrate everything...

Might want to discuss with client to only migrate part of the site and build the rest from scratch. If they have 1000s of press releases etc this is usually prime target for migration while some landing pages etc can easily be recreated by editor instead in new solution.