There is no managed process to migrate a Website from Google Sites to WordPress.com. It’s really a shoveling process – copy and pasting content. The client engaged us to advance the capability of their web presence to support community building.
What’s important to exercise in the process is an intelligent

reorganization of the subject matter.
There are a list of standard “fixed” or static pages — “Contact Us” would be one of those.
Then there are areas of interest best fitted into post categories.
In this example, over a matter of 3 hours, we moved the content,

redesigned the layout and relationships and redirected web traffic.
The addition of tags and correctly relating content to search on WordPress.com resulted in a number of post and page “likes” and that accumulation of attention continues at as I compose this post.