Was your choice of landscape or portrait or square canvas a conscious one, or did you merely pick up the first one that came to hand? Depth or distance is easier to perceive in a wide landscape format rather than a narrow portrait format. Effectively the width of the canvas allows for more components of perspective to tie into the horizon line (the obverse to this can produce a very striking effect, for example "Christ of St John of The Cross" by Salvador Dali).
We also tend to look at landscapes horizontally not vertically, our eye is trained to look at landscapes sideways not up an down. That said, built-up scenes in cityscapes or inside something like a forest benefit from portrait orientation where you're seeing down tunnels of tall buildings or trees.
Don't neglect hard and soft edges. A soft or lost edge will seem further away, as if you can't quite see it. A sharply defined edge will, conversely, seem closer. Don't forget layering neither, the arrangement of elements in layers one behind another with parts obscured. Create the sense of the landscape marching away into the distance.