How to send a push notification to more than one device (iOS)?

Question 1

You should queue a separate notification for each item to process.
It is not possible set multiple device tokens on a single notification. The OperationCanceledException will occur, because you do.

Question 2

Example: Console C# Application

This assumes

you have valid production and development certificates
you have stored multiple device tokens within your database
you have a notification that comes from your database

You are using PushSharp Library

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using PushSharp;
using PushSharp.Core;
using PushSharp.Apple;
using System.IO;

namespace MyNotification
{
    class Program
    {
        //args may take "true" or "false" to indicate the app is running for
        //development or production (Default = false which means Development)
        static void Main(string[] args)
        {
            bool isProduction = false;
            if (args != null && args.Length == 1)
            {
                Console.Write(args[0] + Environment.NewLine);
                bool.TryParse(args[0], out isProduction);
            }
            try
            {
                //Gets a notification that needs sending from database
                AppNotification notification = AppNotification.GetNotification();
                if (notification != null && notification.ID > 0)
                {          
                    //Gets all devices to send the above notification to         
                    List<IosDevice> devices = IosDevice.GetDevices(!isProduction);
                    if (devices != null && devices.Count > 0)
                    {
                        PushBroker push = new PushBroker();//a single instance per app
                        //Wire up the events for all the services that the broker registers
                        push.OnNotificationSent += NotificationSent;
                        push.OnChannelException += ChannelException;
                        push.OnServiceException += ServiceException;
                        push.OnNotificationFailed += NotificationFailed;
                        push.OnDeviceSubscriptionExpired += DeviceSubscriptionExpired;
                        push.OnChannelCreated += ChannelCreated;
                        push.OnChannelDestroyed += ChannelDestroyed;
                        //make sure your certifcates path are all good  
                        string apnsCertFile = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "../../Certificate/Certificates_Apple_Push_Production.p12");
                        if (!isProduction)
                            apnsCertFile = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "../../Certificate/Certificates_Apple_Push_Development.p12");
                        var appleCert = File.ReadAllBytes(apnsCertFile);
                        push.RegisterAppleService(new ApplePushChannelSettings(isProduction, appleCert, "135TrID35")); //Extension method

                        foreach (IosDevice device in devices)
                        {
                            //if it is required to send additional information as well as the alert message, uncomment objects[] and WithCustomItem 
                            //object[] obj = { "North", "5" };

                            push.QueueNotification(new AppleNotification()
                           .ForDeviceToken(device.DeviceToken)
                           .WithAlert(DateTime.Now.ToString())//(notification.AlertMessage)
                                //.WithCustomItem("Link", obj)
                           .WithBadge(device.BadgeCount + 1)
                           .WithSound(notification.SoundFile));//sound.caf
                        }
                        push.StopAllServices(waitForQueuesToFinish: true);
                    }
                }
                Console.WriteLine("Queue Finished, press return to exit...");
                Console.ReadLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
                Console.ReadLine();
            }
        }

        static void NotificationSent(object sender, INotification notification)
        {
            Console.WriteLine("Sent: " + sender + " -> " + notification);
        }

        static void NotificationFailed(object sender, INotification notification, Exception notificationFailureException)
        {
            Console.WriteLine("Failure: " + sender + " -> " + notificationFailureException.Message + " -> " + notification);
        }

        static void ChannelException(object sender, IPushChannel channel, Exception exception)
        {
            Console.WriteLine("Channel Exception: " + sender + " -> " + exception);
        }

        static void ServiceException(object sender, Exception exception)
        {
            Console.WriteLine("Service Exception: " + sender + " -> " + exception);
        }

        static void DeviceSubscriptionExpired(object sender, string expiredDeviceSubscriptionId, DateTime timestamp, INotification notification)
        {
            Console.WriteLine("Device Subscription Expired: " + sender + " -> " + expiredDeviceSubscriptionId);
        }

        static void ChannelDestroyed(object sender)
        {
            Console.WriteLine("Channel Destroyed for: " + sender);
        }

        static void ChannelCreated(object sender, IPushChannel pushChannel)
        {
            Console.WriteLine("Channel Created for: " + sender);
        }  
    }

}