Cats are far pickier than dogs and therefore their food is more flavored, especially with sugars. They're not good for your dog, so try to discourage/prevent eating cat food (and cat droppings).
Have you tried hot water on the Wellness? That has done the trick with my pups. Eventually they seem to prefer it dry, but to start they usually prefer it with warm water.
Do not start catering to finicky eating. Just put the bowl down, and take it up in 15 minutes. The puppy is 8 weeks old and won't starve to death if it misses a meal (are you feeding 3 meals at this point?) The pup will soon learn that food has to be eaten when it's presented or it disappears.
It's not cruel, it's just reality. The more variations you give the pup at this young age, the more picky he'll get and you'll spend even more time trying to coax him to eat. He'll decide that not eating prompts you to add more goodies. He'll just be waiting for the next "offer" since he's learned that the longer he holds out, the better the food gets.
Make it a non-issue -- here's your food. Didn't eat it? Next meal's in 5 hours. Here's your food. Not hungry? Next meal's in 6 hours (assuming you're feeding 3x). It's HIGHLY unlikely the pup will skip more than one meal.
