Hello, my name isXXXXX I can try to help answer your question about Nanook.
He may have developed a food aversion when he was feeling ill and eating the other puppy food. Often when you vomit something, you never want to eat it again, and the same can apply in dogs.
Likely that Nanook will always be a finicky eater, as can be the case in this breed.
In the long run, cat food is not an ideal situation.
You can try going back to the 4 health kibble and try spicing up his meals with a table spoon of low fat cottage cheese mixed into the kibble, and some shredded white meat chicken.
The other thing to try would be a small dab of canned food mixed into the kibble.
Hopefully this helps. Please feel free to respond with further specifics or questions.