Sexing young canaries ?

I have two young canaries. About 2 months old. Has anyone noticed behavior that determines sex before maturity? I heard shyness, size, chatter... I noticed the larger one I believe might be a male, talks a lot, flys all over for attention and starts fight with shy one while in their cage. The fights arnt bad just more flapping a screaming and the dominant one will jump on the shy one. I'm holding off separating them till they are eating seed more. I know a vet can take blood to check gender but I don't want to put them through stress and I have someone who wants a female. Hoping to find out soon so he can finish off the handfeeding so they can bond. I noticed my other grown canaries only like me now and scream if other people try to let them out. Don't want that to happen to these babies. Sorry for the long story.