Yes you can feed sunflower seeds to pigeons and they love them.
I've found that the pigeons here at the park love sunflower seeds so I buy some sunflower seeds to feed to them and enjoy some myself.
The pigeons flock to the sunflower seeds and eat them and they really seem to enjoy them and cannot get enough of them.
I've made friends with Pigeons by giving them sunflower seeds and although in some places you're not supposed to feed pigeons nobody is really gonna stop you.
I've fed Pigeons some sunflower seeds in New York City as well and never had any issue with getting into trouble for it.