public class Product
{
    public int ProductID { get; set; }
    public string ProductName { get; set; }
    public string Category { get; set; }
    public decimal UnitPrice { get; set; }
    public int UnitsInStock { get; set; }
}

public class Order
{
    public int OrderID { get; set; }
    public DateTime OrderDate { get; set; }
    public decimal Total { get; set; }
}

var customers = (from c in dataSource.Customers
                        from o in c.Orders
                        where o.Total > value
                        select c).Distinct();

var customers = dataSource.Customers.Select(c => c.Orders
                                                        .Where(o => o.Total > value))
                                                        .Distinct();