First go to world 4 haunted house, next at mini Mario at the fifth/sixth room jump on the pipe to the next room and kick-jump on the three blocks, then kick-jump through the thin path until you reach the door, finally enter the door to the red flag.
in world 1 at the tower there is a red flag that you need to get to unlock the cannon.
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.
it is not stars it is a world
Get all 150 stars
get the cannon in the worlds
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.
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.
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.
you have to finish the level
I think you mean how to unlock it. -Either complete World 5 by defeating the boss with MINI MARIO. -Or unlocking the cannon on World 4.
it is not stars it is a world
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.
Use a cannon
Complete level 6 sfeb5h6bgtegbu
By going into a cannon
you have to get the red flag on level 3 and then you will a secret level and if you get the red flag on the sercret level ole you will have the cannon but it will not take to world 7 it will take you world 5 the way to get the real world 7 cannon is in wolrd 4