Google Calendar has a feature where you can write a message to your event attendees when they get notified that your event has been canceled.
Step 1 : Click on the event you want to cancel
Step 2 : In the event details panel click the trash icon
Step 3 : In the delete recurring event panel select the This event option
Step 4 : Next fill out the text-area form with the message you want to send to your attendees when you cancel your event.
Once you click send, the attendees will receive a notification email with the message.