I actually try to not expect anything or theorize, so that the development can still surprise me, but Kanjuro being the traitor was not really a surprise. He had the smallest influence overall and made the most sense to be the traitor. I considered Denjiro for a time, but the recent chapters strongly went against that.
It was a kinda long flashback arc and was strong in many aspects, but overall felt weak. Like most of these kinds of arcs it suffers from us, the readers, not having spend enough time with any of the characters, because they mostly only get introduced in the flashback or shortly before and thus the reader doesn't have a strong emotional connection to them like to the mainline characters. Oda really tried to push for that especially with Oden, but it didn't really work as well for me. I felt a stronger connection to Roger or Whitebeard than to Oden for example.