The requirements for uplift are intelligence, speech, and the ability to use tools (dexterity in fingers). It seems that the Puffin Dog has a finger advantage over other breeds. Also the Lundehund has the ability to spread it’s front legs out horizontally and to turn it’s head around to face backwards, both these abilities significantly increase it’s potential ability at using tools (uplifted dogs could use their mouths to manipulate tools as well as their hands).
So we need to find a breed that has good vocal capabilities and a breed that is intelligent and produce a cross-breed that has the best of all three!
Lundehund Syndrome sounds nasty, and would be almost impossible to breed out of pure bred dogs, but when producing a cross-breed it should be easy enough to do. Given that we don’t care whether the uplifted dogs look like Lundehund’s, have the same number of teeth, or are identifiable with that breed in any way other than dexterity it should be easy to breed out the genetic damage.