There's poplars and there's poplars.
In the West poplars mean the genus populus. These are soft wooded fast growing trees that include "white", "balsum" and cottonwood. Good for pallets. Not used for anything fancy.
In the East poplar usually means "tulip tree","tulip poplar"or "yellow poplar. All the same tree genus liriodendrum. Also fast growing but producing a furnicher grade pale wood that lacks distinctive grain. This wood is commonly used for mouldings so we know it works well.
Your best bet is to get a piece of what you're refering to and see how it saws, planes and sands.
If you're going to build anything out of pallets you'd better learn how to scarf. Good luck.
Charlie