Migration form Exchange2010 to Exchange2013

Hi,

I have a plan to upgrade Exchange 2010 to 2013. In Exchange 2013 system, I'll have 2 CAS server and 2 Mailbox server.

I know that the CAS server in both version will handle the move request, so the CAS2013 server will take the MRS when I migrate mailboxes from Ex2010 to Ex2013.

Now I have a question:

- When I do my migration by using seperate power shell command instead of using bulk migration in 2013 ECP, one CAS server or both CAS server will do this job?

- Can I define which CAS server doing the migration job?

Thanks,