Most Cavadors are breed from a Labrador Dam (Mother) and a Cavalier King Charles Spaniel Sire (Father).
There are a couple of reasons for this but mostly have to do with the size difference of the two breeds. Some litters will be from natural insemination where as some will be from artificial.
The reason that Dam should always be the Labrador is because a 60-80 pound lab shouldn’t have any difficulties giving birth to puppies that will be 30-40 pounds as adults. However the other way around that same is not true. A 18-22lb Cavalier dam would likely have serious problems giving birth to puppies that will likely weigh between 30-40lbs as adults. Cesarean Sections would be likely, just wouldn’t be healthy for mom or the puppies.
Second Generation puppies (F2) would be the offspring of a Cavador bred to another Cavador. This can be a bad idea for a few reasons. Firstly when a lab breeds with a cavalier the puppies all get one small gene and one large gene. This is over simplified and not actually how it works but for the purpose of this explanation it will do. Therefore all of the puppies will be close in size, with and average around 30-40 pounds. If one were to breed two cavadors there is the possibility of an offspring getting a large gene from mom and a large gene from dad, and therefore having two large genes and being close to the same size as a Labrador. OR an offspring could get two small genes and be close in size to a cavalier. In this litter the puppies would likely still have the same average weight (30-40 pounds) but there would be a much larger deviation in the size of the puppies. Some could weigh as much as 70 pounds full grown and some as small as 18 full grown. So this would not be good for the puppies. Also it would not be good for a 30 pound Cavador mother to try to give birth to a puppy that will weigh 70 pounds full grown (again may require a cesarean section.)
For this reason all Cavadors should be Spayed or Neutered after a year or two or once fully matured.
If for some reason someone feels as though they MUST breed their Cavador. I would suggest the following.
A Cavador female could be breed with a Cavalier Male to make a F1b crossback cavador. This would technically be 75% Cavalier and 25% Labrador.
A Cavador male could be breed with a Labrador Female to make a F1b crossback Cavador. This would technically be 75% Labrador and 25% Cavalier.
In both situation the mother would safely be larger than the puppies.
F2’s and F1b’s will not have all of the advantages of hybrid vigor, and that is why any perspective buyer should always first consider an F1 hybrid. Ask a breeder if they breed first generation or multigeneration Cavadors.