Chagaev was always a tough, world class operator. Whyte seems good but I'm getting a whiff of the glass jaw from him. Could be wrong, but being less than teak tough is not good against Chaggy. I would likewise pick Ruslan ftw, at this point, anyway.
Let's take it as Chagaev at the time he won the WBA belt (which they eventually stole from him). Chagaev would either easily outpoint Whyte, or stop him.
Chagaev prime was better than any of Whyte's wins. I know he was a bit past prime but still not sure how he lost to Browne when he was beating the crap out of him. Should have went to his glass middle. Hindsight is easy though.