the File acknowledgment number is the CANT### . I dont know what is the online reg # but don't need it if you have CANT.
Just an update for others, went last week for walkin surrender+ OCI application, BLS (Toronto) didn't take any original docs other than the Indian passport being surrendered. We even took notarized copies as didn't want to submit originals but they didn't need it (wasted $$). We opted for pickup so I guess will go pickup the surrender envelope and another empty envelope . Also for OCI, we got the CANT## number right away, which can be used to track on both BLS and the India Gov website (although I think India Gov will have more detailed updates).
Unlike before, I feel attitude has improved and they were more friendly (and no frowns when we asked for pickup instead of delivery...maybe we got lucky lol).
BTW the cybercafe next door certainly helps to avoid another trip.