Blanchan, Blanchamp, Blanchant, and Beauchamp (see the unmerged match of Beauchamp-111) are all variations found for this name. A transcription of the record for his son's marriage has Anthoine Blanchamp [Blanchant], which would seem to indicate that the transcriptionist thought Blanchant was the correct spelling.
I'm thinking that Blanchamp or Blanchant would be better than Blanchan, but I'm ok with the father remaining Blanchan. If anyone has a source that indicates how Leonin spelled his name in his lifetime, that would be great! (and the best spelling to use for the WikiTree ID).
Thanks! Liz