If this is the food it sounds like a good food:
Vets Choice: Products - Holistic Health Extension Original
Some foods are too high in protein but this one seems okay. You are lucky he did not like the Beneful or the Purina because those are not really good quality dog foods.
It is possible the canned food could be causing him stomach problems. I know mine do not do well if I add different kinds of canned food to their diet. I just use Pedigree Healthy Digestion and Pedigree Chopped Chicken and mine all do well with that so I don't switch around. I really just add enough to make the dry food a little moist. I know mine do not do well with anything with beef in it.
Sometimes a poor appetite could be due to him teething or it could indicate something more serious. If it continues then you probably should take him in and have the vet do some bloodwork just to make sure everything is okay there.