I have an EXTREMELY picky eater - any suggestions?

You could try Hill's Prescription diet I/D. I worked at both an emergency and primary care veterinary hospital and with all the dogs that came in sick, not many would resist this food. You have to get it as a prescription through your veterinary office but if you ask your vet i doubt they would refuse to let you try it. However, my dog sometimes goes a whole 2 days without eating occasionally but she is 50 lbs.

Is he active? Whenever my dog stops eating it's because my routine walking stops (like when I broke my finger). Maybe you might want to try routine exercise to raise his metabolism so he gets hungrier more often? Worth a try! My dog seems to have more appetite if we get more exercise.

Hmmm...strange. I wonder if he is getting food from neighbors or is also getting fed by another family member.

Some pets seem to become pickier the more you change their food. I would suggest choosing one food (whether it be dry or canned), that is a good quality maintenance diet, and sticking with it. You can use either the free feed method (put a meal in his bowl and let him eat it at his leisure) or the meal-feed method (Put a meal in his bowl and leave it down for a certain amount of time, maybe 15 minutes. If he doesn't eat it...oh, well. Take it away and he doesn't get another shot at it until the next meal time.) Since the vet says he's not underweight, I don't think you have to worry about him starving. if you do notice him losing weight, then something else will need to be done. But I suspect if he's left to his own devices, he'll decide to eat.