Poor little guy
The switch ( especially a drastic one like that ) can be hard on their tummy . What was his old food that the vet didn't want you mixing with it ?
Do you only want him to have canned food ? If you don't mind kibble maybe you can start with Evo kibble and mix it a bit with his old ( dry? ) food then when he is switched over and doing well on the Evo dry kibble you can start adding a bit of Evo canned to it , and eventually switch over to all canned if that is what you want to do.
I feed wellness core kibble and I also use the Wellness grain free canned. I take a small amount of their daily portions of kibble and mix it with a small amount of canned food for their breakfast meal...then a bit later I put the rest of the kibble down for them to have throughout the day ( I free feed ) I like feeding both . I wouldn't like just canned unless mine couldn't eat kibble for some reason, but that is just my preference.