do you have exchange 2010/2013 or O365? you can create an AD group and populate it with the users to be journaled. then you configure your journal connector to journal the group and the target address is the EV.cloud smtp address.
I'm trying to determine if selective journailing as described here for on-prem (http://www.symantec.com/connect/articles/selective-journaling-enterprise-vault) is an option on an EV.Cloud configuration. Nothing in the documentation points to it being available but we have a strong business case that requires something similar to selective journaling and this doesn;t look possible as stands with EV.Cloud
As Tony mentioned, you cannot selectively journal without the email server journaling only the messages from the email accounts that you have segregated to be journaled.
However, you can selectively archive which mailboxes from the journal stream. By creating disable accounts for the email accounts that you do not want to archive, you can selectively archive only messages from those enabled archive mailboxes.