would a sun leaf have more open or closed stomata, and why?

Answer 1

since stomata regulate O2 and CO2, in the light the majority of stomata should be open to facilitate photosynthesis.

Answer 2

Do you mean a leaf that is in the sun?

Leaves in the sun would have their stomata open in order to exchange carbon dioxide and oxygen with the air during photosynthesis. The stomata open because the guard cells that control the opening have chloroplasts of their own and the light leads to a chain of events that ends with swelling the guard cells and opening the stomata.