GetEnumOrder.cs

IEnumerable<T> GetEnumOrder<T>()
{		
	var type = typeof(T);
	var tmp = new List<dynamic>();

	foreach (var value in Enum.GetValues(type))
	{
		var attr = type.GetMember(value.ToString())[0].GetCustomAttribute(typeof(DisplayAttribute), false) as DisplayAttribute;

		tmp.Add(new
		{
			Value = (T)value,
			Order = attr?.Order ?? 9999
		});
	}	
	
	return tmp
		.OrderBy(t => t.Order)
		.Select(t => t.Value)
		.Cast<T>()
		.ToArray();
}

TestEnum.cs

enum TestEnum
{
	[Display(Order = 0)]
	One,
	
	[Display(Order = 2)]
	Two,
	
	[Display(Order = 1)]
	Three
}

Usage:

var list = GetEnumOrder<TestEnum>();