you have to finish the level
you can unlock a level with a pipe and cannon around it (i got it on a red flag on world 2 number 4 ) and finish that on a cheat flag( the yellow pipe above the other 1). this will unlock the cannon.
Complete level 6 sfeb5h6bgtegbu
You go to the midway castle
in world 1 at the tower there is a red flag that you need to get to unlock the cannon.
it is not stars it is a world
It is a random item drop
To go in to world 5 ina wrap cannon on wols 2 you must do 2 short cuts!
Dude you buy it duhhh
get the cannon in the worlds
Go into the first castle and when you get to the partwith the 4 rows of falling blocks run and jump at the black part of the left wall.
Hack the program
To open the world 4 cannon in the super Mario brother's game DS, you have to enter through the last level of world 2. Make sure you have a blue mushroom, which makes you smaller. You can do everything in this level normally until you get to the end. There will be a Caterpillar-like creature waiting for you. You have to turn into a smaller version of Mario (using the blue mushroom) and defeat the creature. After you are done, the sign which says world 3 will turn around and read world 4. You will automatically go through a small hole and will appear in the exciting jungles of world 4.