Agreed, Jen. Canon is in the eye of the beholder. Until a new Enterprise TV show or movie comes out to contradict what unfolds in the books, the books are part of my canon.
Re. Trip's working for Section 31 as a Romulan infiltrator: I like it!
In a series that has technology that allows instantaneous translation of different languages, not to mention matter transmission and FTL travel, I don't think it is a stretch to have a human surgically altered to pass for a member of an alien race.
For me, one of the most fascinating periods of Trek history is the time spanning the creation of the United Federation Of Planets and the Romulan War. This book seems to be leading in to that story perfectly. And given the fact that we don't "officially" know what Romulans look like until the TOS episode "Balance Of Terror", I think the authors have created an incredibly effective plot device. They not only bring back a beloved character, they allow us to vicariously meet the Romulans face-to-face for the first time. And considering the ramifications of finding out that such a menacing race is possibly related to a founding race of the fledgling Federation, I think the writers have set up a very plausible explanation of the discrepancies between the "official" record of events and how they occurred in "real life".
As of Chapter 15 of the book, the proposed Coalition Of Planets is on shaky ground. If it had become public knowledge that one of the main members (the Vulcans) were related to the Romulans, the Federation may have never come into existence. Although this hasn't been brought up in the book yet, and possibly won't be addressed, I can see this as being justification for a cover-up. Hence the whole "Trip's Fake Death" and "Shran's Fake Daughter" issue.