Tawawa

This doesn't work because, according to the condition, the cart needs to be returned each time.

This works because the condition doesn't mention any cart that needs to be returned. The only cart mentioned is a descriptive element about transporting canvases that cannot be carried by hand.
Crossing the border means passing through a checkpoint by showing a passport. Since only people can cross it, and luggage needs to be transported, the question is how to transport each inanimate item with the help of a person in the correct order, preserving its integrity.