I have setup Marketing Cloud Connect app in my Salesforce org and also setup Salesforce Integration under Marketing Cloud (Email Studio -> Email -> Admin -> Salesforce Integration). Now, when I go to Contact Builder -> Data Source -> Synchronized tab, I'm not able to sync the custom object (Campaign__c). It just allows me to sync Contact, Lead, User object types.
Is it possible that I might missed something while setup which preventing the sync for the custom objects? How does an object become available for synchronization? let's say if want to synchronize Account, how can I achieve that?