I have read that anal intercourse increases risk of anal cancer. What about anal stimulation by partners finger? Going no more than an inch or two?

Clean hands. The same virus (hpv) that can cause cancer from unprotected anal sex can also be transmitted by fingers. So safest is not to have that contact. But if you choose to, very clean hands, consider even a condom on the finger.
Probably less risk. However, digital stimulation can still cause tears, pain, inflammation and bleeding. Generally, the anus was designed as an exit and not an entrance. Good rule of thumb to follow in my opinion.