They both scream too damn loud. Who do you think would win?
I don't know too much about Black Canary but from what I've read on her, I think Siryn would win. She has developed her powers quite far (deafening others, flying, hypnotic trances), in my opinion, further than Black Canary seems to have. I could be wrong, though.
Siryn can fight too, though not as well as Black Canary. Siryn learned to fight hand-to-hand when her throat was slit by Feral in X-Force and when she was being dragged around by Black Tom. Siryn has refined her sonic scream to where she can fly, has an enhanced sense of hearing, use it for echolation, hypnotize others, deafen them, render them unconscious or dead, shatter or liquefy objects, and even deflect lasers and neutralize jets and stuff. She's stronger, power-wise and control-wise, than her father, Banshee.
Now, I love Black Canary and she can kick some butt. Her Canary Cry may outpower Siryn's sonic scream one-on-one. but Siryn is resourceful and isn't dumb. For example, she can enthrall Green Arrow, Wildcat, and other members of the JLA to attack her. Plus, Siryn can fly. If it was just a hand-to-hand thing, Black Canary would demolish Siryn.