I haven't heard any inside reports. You're quite right, though, that there was a 90-day consultation period before Canada joined, and they didn't join until the end of the second round. I'm not privy to what may or may not have been agreed to during those two rounds.
During that period, Canada did not have access to the negotiating text. Now the same condition has been imposed on Japan. It does not have full access to a negotiating text until it joins the negotiations at the next round. There has been some flexible scheduling of the next round to enable Japan to participate. Again, that did not occur in the case of Canada.