Exchange 2013 between two Sites

Hi 

Due to the two businesses being owned by the same company, i would like to plan a setup whereby there is an Active Directory Server and Exchange Server at Each Site.

Site A: Exchange 2013 CAS and Server 2012( maincompany.co.za )

Site B: Exchange 2013 CAS and Server 2012( secondcompany.co.za )

Each Company has a different Domain name and users specific to each domain

There will be a link between the servers over the internet (Private network)

my question is: would this be possible? and if so how would the AD config and Exchange config be setup?

Thanks

darryl