Kingfisher,
I suppose well cleaned used gallon paint cans would be OK, but I would recommend new unused paint cans.
When you make the holes in the paint can lid they need to be very tiny. I make about 10-12 holes in a gallon lid. I hold a tiny bee hive frame nail with a pair of needle nose plires, put the lid outside down on a block of wood in a vice, and tap with a light hammer. The hole I make is only point size and not the diameter of the nail. The holes made from the inside to the outside provide a "burr" for the bees to hold on to when they draw the syrup out.
When you invert the can over the hive there will be some leakage, but it will stop. Changes in barometric pressure will also cause some leakage.
Good luck feeding and have agood productive year.
Steve