Affixing a sail shade to balcony railing with a pole
Generally speaking, when the wind gets behind a sail, it exerts considerable force. People have crossed hundreds of miles of ocean with no more than 3m x 3m x 3m.
If you manage to affix the corner of the sail firmly to a sturdy pole and affix the pole immovably to the railing, you may be rewarded with the sight of sail, pole, railing, and all soaring off over the courtyard. Even if it doesn't actually break, your landlord is not going to be happy about what happens to that railing.
I checked some online introductory sail and rigging tutorials. According to their calculations, if a gust of wind is deflected by your building and strikes your sail nearly upward (or downward) at about 35 mph, the force exerted by each corner of the sail upward (or downward) would be about 200 pounds.
The structure that is least likely to damage your balcony is a full pyramid. Find two rigid lightweight poles each 3m long, attach them together at the ends, and form them into a triangle based at the pre-drilled holes. Prop up the free end of the triangle with a third pole, with its bottom attached to the base of one of the railing stanchions.
Attach the outer corner of the sail to the place where the three poles meet.
Do not brace the vertical pole against the railing. Let its motion be constrained entirely by the two poles along the sides of the sail.
Note that whatever fixtures you install at the locations of the pre-drilled holes will also have to hold against momentary upward (or downward) loads of 200 pounds.