Going back to the grain free diets and dietary-induced DCM issue Aru mentioned further upthread (though acknowledging that the whole issue is still to be taken with a pinch of salt at present), Acana is #1 in the list of suspect diets due to a very high legume content.
Grain allergies in dogs, and food allergies in general are actually quite uncommon - other than wheat (15%). Most dogs actually have contact allergies, which can be diagnosed with a skin prick test and often the best treatment is a course of tailored immunotherapy injections.
I would definitely avoid anything with peas or lentils in the ingredient list as a main source (first ten) as this seems to be the link with the DCM issue.
My dog with allergies does well on James Wellbeloved Turkey and veg or salmon and veg (grain free). My vet said those two flavours are the best as lots of dogs react to chicken or red meats too. You have to make sure any treats or chews match the diet too.