If you had a cannon dream, it can mean surprising news. Dreaming of a cannon carries the meaning that is related to its real life traits. Thus, the cannon dream means you will see or hear a big boom, followed by a projectile. A cannon is fired to commemorate an important event. This will be the big news.
If you dream of seeing a cannon in a circus, it means you might get a surprise in your waking life. This flying surprise is likely to be an airborne letter or parcel. You may expect an airmail letter, postcard, or parcel.