First off, I haven't been on my trip to the Maritimes yet so I can't comment on the accuracy of the book. I always get the Lonely Planet guide for wherever I'm traveling to, because it's always so helpful, particularly with what neighbourhoods to stay in and what sites to see. I haven't been on my yet, but using this guide has helped me figure out how long I want to stay, which provinces to hit up and what I want to see on them, and what cities I'll be staying in. So, so far so good.
Cons: I would have liked to have seen a few more photos in this particular book and a bit more detail on getting around and back and forth between the provinces. The book also seems a bit sparse as far as history and background compared to other Lonely Planet guides. I know it's Canada, not Egypt, but there is history to be had in these areas and I feel like I'm still going to have to do more research on some of the sites.
UPDATE: I did go on my trip and did find the Lonely Planet guide helpful, as always (I just bought one for Greece, too so "squeeee!!!"). That said, I stand by my observation that there could be more on the history, as the Maritimes are one of Canada's richest places...well for history at least... More on pirates and swashbucklers, please!!
The one thing I also heartily agree with that I think they could stress more is the fact that the BEST way to see the Maritimes is to rent a car. It's so small and so beautiful that some of my favorite parts of the trip were just when my husband and I were driving from town to town. It's really hard to get lost (seriously, on PEI, just drive another half hour and you'll hit the water on one side or another), and traffic there is so easy that it's probably less stressful than rush hour anywhere else in the world.
Also, most of the charm of the Maritimes is its beautiful landscape and awesome food. The Lonely Planet guide doesn't mention it much, but really look for Happy Hour specials on seafood to save $$$ (like a lb of mussels for $6 in Charlottetown or 12 oysters for $20), so find a cafe with chairs overlooking the ocean or the street and prepare to hang out awhile.
And if you happen to be Gluten Intolerant or have Celiacs - oh my god is the Maritimes like heaven!! Almost every restaurant has a GF menu (GF fish and chips in Charlottetown!! GF bread in the pubs of Wolfville, and GF pasta in Halifax = GAHH!!)