Boxer has upper mouth sore

Question
Our Boxer has a dime size pink open lesion / on the roof of
his mouth.  Can you advise us on care and or tx?
   Thank you.

Answer
It can be a canker sore caused by a virus, an insect bite, food allergies, or  papiloma to cancer.

Only a vet can tell for sure.

Has he been stressed? Any changes in the family? A different diet?

I would take him to the vet as it can also be a symptom of kidney failure--