Entertainment Earth has a new listing for Transformers: The Last Knight Role Play Items. The items include Optimus Prime’s Sword and Bumblebee’s Cannon.
While there isn’t any available image for the cannon, the sword however seems to be a direct repaint of the Transformers: Age Of Extinction Optimus Prime Deluxe Light and Sound Sword. Therefore we can assume the cannon would be the same.
According to the official description, the sword measures about 25-inches long and the cannon about 11-inches long x 5-inches wide.
Check out the listings at EE: