If you aren’t in Canada, all those Acanas won’t be available to you-none of the Acana Classics, just Singles and Regionals.
With over a mile a day and some fetch, I wouldn’t be super concerned with fat unless you are seeing a lot of weight gain. Not only has high protein % been proven, it’s recommended for senior dogs. So if he is fine on the high protein, keep it up.
I would try out a novel protein, and I would try rotating through proteins that he works just fine on, it will help keep him healthy. Of the things you listed, the acana you may not be able to find, and in my opinion, Taste of the Wild and Merrick have too many company issues to bother with, especially with a dog you are trying to pinpoint some stomach issues, it may throw off your findings unnecessarily. Wellness is nice, Acana and Orijen are Nice, Earthborn is nice-and they have the primitive naturals that is poultry based and over 40% protein as well
