cannon, canon, canyon

Cannon or cannon means the large mounted gun  you might see used as a war memorial on a courthouse lawn--
They fire the cannon on the courthouse lawn every Fourth of July.
The story of Molly Pitcher taking her husband's place and firing the cannon is genuine history.

Canon or canon ( rhymes with cannon ) means the body of church law or rules, or a member of a certain religious order--
They ran in late for Sunday services and the canon scowled at them.
They are very religious people, and will not divorce unless they can do so under canon law.

Canon is also used to mean the accepted set of rules or works of reference of a particular discipline or area of study--
These history books are no longer accepted as part of the canon.

Canyon or canyon means a  valley or gap with steep sides, as  between two mountains or cliffs--
We are going to drive out west this summer to see the Grand Canyon.
This canyon looks familiar. Maybe they have used it as the set of a TV western.

Now that you know that, you can say--
"If you fire a cannon in the canyon, the echo might reach all the way to the cathedral, where the canon could hear it."

Note--you may see "canyon" spelled "canon", but with a tilde ( ~ ) over the "n". This is the Spanish spelling of canyon. We borrowed the word from the Spanish who had settled in the American West and named its geographical features. Most American keyboards don't have a function for putting the tilde ( ~ ) over the "n".