If you are using Dovecot on both machines, then it is simply a matter of copying the data once the email accounts already exist on the cPanel machine.
If you are using a control panel that we support for migrating (Plesk, Ensim, DirectAdmin), then we could assist with the migration for you. If you aren't using one of the supported migration control panels, then we can help to answer questions, but we wouldn't be able to perform any of the migration work itself.