The writing is fine, the plot decent - but after 400+ pages, you'd like to think the characters had accomplished something.
I don't understand how a post-apocalyptic society — even one run by an oppressive, anti-scientific, church — which is in continual war with its neighbours, could fail to progress scientifically — at least in the field of war. At least, in George Orwell's 1984, the three mega-powers clearly want a stalemate. In this book, America is trying to win its war: how is it not possible that they have at least reinvented the hot-air balloon to provide spotting for artillery?
Finally, an American who has made his home in Canada should recognize just how repugnant is the idea that Canadians would willingly become part of America. Wilson doesn't even try to explain how this could come to pass, but that isn't enough! He then places a significant part of the story in Quebec, and there isn't a single French terrorist. Many French Quebecers can't stand the thought of being part of Canada, with language rights. They will never tolerate becoming part of the US with no language rights at all.