This stage is Super Mount Beanpole (1-3). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars.
Game Play Walkthrough Video
Green Star 1
When the course begins, immediately climb the tall tree on the left to find the first green star.
Green Star 2
Hit the POW block at the third horizontal row of moving blocks. Go inside the pipe to unlock a small mini game. Collect all the blue coins for the second green star.
Green Star 3
After bringing up the platform with the pawprint, you will get to the sky with a small obstacle course. Hit the invincible super star to clear it quickly. You will obtain the last green star at the end of the course.
You can obtain the stamp next to the pipe of the second green star.