How do I initialize transactional replication from a backup at a URL?
This is a very good question but at the moment, initializing a subscription from a backup stored in Windows Azure Blob storage is not currently supported. I believe this would be a very cool feature for replication and I'm sure the folks at Microsoft would agree. I suggest proposing this idea on UserVoice.

However, since you've already restored the backup, and the schema and data are already in place at the subscriber, try executing sp_addsubscription with the @sync_type of 'replication support only' and see if that meets your needs.

More details for initializing a subscription manually can be found in How to: Initialize a Subscription Manually.