for with you can use
var datas=(from d in entityObj.GetDataFunction into somename select new{somename.ID,Somename.Name....});
and for Union
var data1=entityObj.GetFirstData.Select(x=>new DataDto{x.Id,....});
var data2=entityObj.GetSeconddata().Select(x=>new DataDto{x.Id,....});
data1=data1.Union(data2)