
You have left it too late in my opinion.
If you are needing to ask on here then you as yet do not have sufficient in depth knowledge about the breed, and the bloodlines to be considering breeding a litter.
Breeding requires knowledge, and if you haven't got it, then you need to woirk with someone who has, usually your bitches breeder if reputable.
I am assuming that your bitch ahs alread had good results for her Hip and Elbow scores and been eye tested clear? Also that she has proved herself a very good specimin in either the working arena or showring, but I suspect if she had you would already ahve yoru eye on likely studs you have seen?