You can use any of the following way:
First Way:
1. Move Site collections from content DB to separate content DB. (http://technet.microsoft.com/en-us/library/cc825328%28v=office.14%29.aspx)
2. Take backup of this new Content DB and restore to SharePoint 2010 SQL Server.
3. Once restoration done. You can moun this content DB to new Web Application at SharePoint 2010 Farm.
Second Way:
1. Take backup of whole Content DB and move to SharePoint 2010 SQL box and restore there.
2. Once restoration done, mount that content DB to SharePoint 2010 Farm Web Application.
3. In this way all site collection come to Sharepoint 2010 Box. Then after you can delete those sites which you dont want.