The ledgerId in Canton is currently hard-coded to the participant.uid.id. You can configure your own .id by manually initializing your node: Canton Console — Canton 1.0.0-SNAPSHOT [0J documentation
For this, you have to turn of auto-initialization by setting canton.participants.<p>.init.auto-init = false
But then you need to manually allocate keys, issue the certificates etc. I actually wrote it up here: Canton offline key for static participant ID - #2 by Ratko_Veprek