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.
you have to finish the level
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.
it is not stars it is a world
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.
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