Synchronization: iMessages on Mac not iPad
No, there will be no sync.
Only the devices, that are registered on iMessage at the point of time, when the message is sent by the sender, can receive the message (technically). The messages are end-to-end encrypted for each receiving device.
In other words: Your new device can't decrypt the old messages, as the original sender didn't know about this new device.  

See this article:


  You’ve actually got one set of keys for each device you add to iCloud,
  and each iMessage is encrypted independently for each device. So if
  you have two devices — say, an iPad and an iPhone — each message sent
  to you is actually encrypted (AES-128) and stored on Apple’s servers
  twice. Once for each device. When you pull down a message, it’s
  specifically encrypted for the device you’re on.


Apple's Security Paper