Other than rumours, speculation and unverified sources, he has not publicly stated whether he has been circumcised or not. Justin Bieber was born in March of 1994 in Stratford, Ontario, and while circumcision was offered free of charge at this time, as low as 29% of baby boys in Ontario, Canada, were circumcised, but this is not conclusive.
Yes he is. I read on another site that pulled copies of medical records of him during his stint in the hospital. He was listed as "no circumcision performed after birth" at his birth-place hospital.
I think he is uncircumcised.