Any3-2

Either character is viable in this level - While Checkers is likely slightly faster, Marbles is a bit easier. This level features a bottom corner clip to go under the train, which not only avoids the difficult platforming inside the train but also saves around 2.5-3 seconds due to not having to backtrack through the bee car. After the tough platforming section on top of the train, there are two methods to optimize the transition to the final area depending on which character is in front.

Optimal - Checkers route

Pay close attention to the bottom corner clip at the start - it is not a typical wall clip. With Marbles in front, line yourself up in the corner facing left, jump and swap when you land and see Marbles get "squished." Do not press your right + swap "clip button" as this will move you right, often causing you to get stuck in the wall and requiring another swap to get out.
You must pass the "bee wagon" before going back inbounds. This is the second wagon with coins under it, and you will hear the bee buzzing sound. If you go to the next car, not only will the bee car repeat, but it will also require you to travel through it and back (the casual route), losing several seconds.
You must travel slightly right from the second ladder to trigger the bonus. The distance you need to travel is only a few pixels - you don't need to enter the car. See the images below for the lineup.
Use the bonus entry jingle to time the pause to exit the bonus. You can pause when you hear the 4th note of the jingle play.
Carefully study the route on top of the train - it's difficult, but can become consistent with practice. If you're not comfortable with it, it's relatively easy to find a piggyback/quad jump route over the enemies that only loses a second or two, or try the Marbles route.
The transition to the end triggers at a point slightly past the cannon. The transition puts you at a consistent horizontal position but does not reset your vertical position. Therefore it's optimal to jump past the cannon rather than going directly into it. After triggering the transition, go back into the cannon to gain height. You want to dropdash near the top of the screen to "yeet" yourself directly into the final train car. See the images for setups.
If you line up the "yeet" perfectly you can make it to the goal with a single roll, otherwise you can do one more dropdash.

Marbles route

As Marbles is required in the next stage, this route does not lose much time compared to the Checkers route. Choose whichever one is most comfortable for you.

The clip at the start is exactly the same. You can swap to Marbles before passing under the train or after.
It's possible to pass under the second frog on top of the train, but also common to collide with it. Be prepared to adjust your timing in case you hit the frog and generate freeze frames.
With Marbles, going in the cannon is quite slow. Instead it's best to just run past it, jump before the transition activates and glide to the end.

Any time of 34 or better is good on this level.

Setups

You don't need to go very far right to activate the bonus. These two images both succeed in activating it.

You don't need to go very far past the cannon to activate the transition.

You want to position yourself near the top of the screen for the dropdash yeet.