Are your pendant lights line voltage or low voltage. If they are low voltage then they need a transformer. The transformer can be put in the electric box in the ceiling if there is enough room- then you could use a flat canopy. If there is not enough room in the electric box in the ceiling then you would need the dome canopy to house the transformer. My pendant lights are low voltage and the transformer is in the 4 inch electric box in the ceiling. I don't remember if they are 12v or 24 volt. The spec sheets for the lights should tell you the voltage the lights use.

Right now we have a big florescent light near the area but an electrician will be putting in the lights, so right now, I don't know that there is a voltage.

My 3 pendant lights are each connected to their own 3 inch electric box in the ceiling. Each has a flat jack canopy. The transformer came with the jack but is mounted in the electric box in the ceiling. If the electrician is not opening the ceiling to add electrical connection boxes the dome canopy which house the transformer might work. If you are going to buy line voltage pendants you don't need to worry about transformers.
You could also post your question on the lighting forum page