Cavity nesters are not too interested in your fancy woodwork, but the size of the entrance hole is really important to them. Waterfowl seem to prefer an entrance that is just big enough. Some birds will inspect several houses before deciding on their preferred nest. You may wish to give the birds a few to choose from, there is bound to be one site that everyone wants to use.
If you are planning to make boxes this winter, this rough guide may be helpful:
3 1/2” Ringed Teal, Smew and Hooded Merganser
4” Wood Duck, Mandarin, Brazilian Teal, Chestnut-breasted Teal, Lesser Whistling Duck
5” Spotted, Eytons, White-faced and Fulvous Whistling ducks, Goldeneye, Goosander
5 1/2” Black-bellied and West Indian Whistling Ducks
6" for the shelducks, who like to nest in burrows