Of course he will love his child as much, if not even more. When the baby arrives, I'm pretty sure his attention will be nowhere else but the baby (and you). Right now, I think, since baby is not physically there yet and he can't hold, feel, smell, kiss his baby, he is merely expressing his paternal instincts on his niece. As soon as baby arrives, those instincts will naturally be imprinted onto his and your child. Don't worry too much about it, take it like he is practising his daddy duties on his niece. Alot of us non-parent folk will agree that this transferring of love happens every now and then. I don't have a child yet and I am attached to my best friends' babies and spoil them silly but that doesn't mean I will not be the same way with my own child one day.