The EventCalendar feature is not designed to be re-used in a usercontrol, it is a self contained feature. Internally it uses a control named DataCalendar, and you can use this control in a custom feature but you would have to bind it to your own data.
You can study the included EventCalendar feature and see how to use the <mp:DataCalendar control by looking in mojoPortal.Features.UI project in EventCalendar/EventCalendarModule.ascx
Hope it helps,
Joe