Liquid food and water are going to be okay for his crop. Solid food could be a problem, especially since he won't be able to eat grit to help digest it. It's important to keep feeding him so his body can help fight these issues attacking it.
Canker often, not always, has a bacterial element to it. If you have the antibiotic, I suggest using it, even though you don't know for sure he's fighting bacteria along with the canker. It's just one more way to give him an advantage over the issues plaguing him.
Those bird meds are fine for chickens. We use fish antibiotics all the time, and often also use pigeon meds. Domestic chickens don't seem to rate their own labels on meds for some reason. Maybe because we eat them.
Canker often, not always, has a bacterial element to it. If you have the antibiotic, I suggest using it, even though you don't know for sure he's fighting bacteria along with the canker. It's just one more way to give him an advantage over the issues plaguing him.
Those bird meds are fine for chickens. We use fish antibiotics all the time, and often also use pigeon meds. Domestic chickens don't seem to rate their own labels on meds for some reason. Maybe because we eat them.