Outlook doesn't support canceling meetings or appointments; you're expected to delete them when they are cancelled.

If you don't want to delete the meeting or appointment, one workaround to assign a category to cancelled meetings and then use custom views to apply a colored label in Day/Week/month view or use a strikeout font attribute in table view to items using that category.

Open the Define Views dialog and Create a new view or Modify the current view, adding Automatic formatting rules to change the text format or apply a colored label.

If you aren't sure how to customize a view, see http://www.outlook-tips.net/howto/custom_views.htm