
Unless very poorly reared, size and substance are genetic AFAIK. If the dog and bitch are suited for size then ideally there should not have been a huge difference between them, i.e. if a smaller bitch were mated to a dog on the smaller scale then pups would be more likely to be mid range of parents. Using a much larger animal of either gender doesn't produce mid-range sizes, but extremes of both.
If this is specifically a show puppy the best information will be available via the local breed club on what litters are available or planned in the near future and you'll be able to find out directly from those on any lists whether there is a waiting list for their litters, what your chances are of getting a pick of bitches that shows potential for the ring etc.
As this will be a member of your family for 10-15 years, it's well worth doing your homework and waiting for the ideal puppy :)
HTH, Teri