I have two 55-gallon industrial heavy duty plastic drums that have been professionally sanitized.

Because the boundaries of my home has yet to be determined, I can't plant in areas I want just yet.

So I was thinking about planting trees in these drums and placing them in the area that is unused but could possibly become a part of my land. If I'm told I cannot purchase the unused land, I'll simply remove them.

Should I use regular soil or potting soil?

I would use potting soil, but since they will not be staying in the pots very long it probably does not matter. Are these trees in pots already or bare root? Also how tall/old are these trees.

If you are planting citruses, you must be aware of overpotting problems observed by Millet and others that have been discussed thoroughly in this forum.