St Peter's is the canal/lock into the Bras d' Or lakes. The marina is on the lake side of the lock. It is a fairly short walk over the road to the marina. Kinda up the hill, across the road, into the marina. I can't recall
if there is a path along the canal/lock. I kinda think there is but I'm not sure.
When you come into the lock you tie up to await being locked through. They will also raise the bridge, hand operated.
I'm Canadian registry so I didn't have to go through the reporting in procedure.
And, to be clear, there are only two navigable entrances to the Bras d' Or, St. Peters and Big Bras d' Or, which is around Pt. Aconi. I think you would have to work at it to have to clear in at Sydney
or any point East of St. Pete's.