It is an interesting consequence of the new reconstructions of the early history of Israel that the Israelites must originally have been Canaanites. Nevertheless, an outspoken hatred against Canaanites permeates the Old Testament. Lemche presents a new way of explaining the anti-Canaanite sentiments of the Old Testament historians, while at the same time disclosing some of the aims and ideas which governed Old Testament history writing.
The first two chapters, on the appearance of the term "Canaanite" in general aNE lit from the 2nd 1st millennia were quite helpful. There he demonstrates that "Canaan" was only a very loose geographical designation, no one (be they Syrian, Phoenician, or Ugaritian) thought of themselves as Canaanites, and there was no monolithic "Canaanit culture." These two chapters are worth your time.
Once he starts dealing with the biblical material, however, the usefulness of Lemche's work depends entirely on whether you can agree with him that the Pentateuch and the Deuteronomic historical books, in their entirety, are exilic at the earliest, but likely even post-exilic. This leads him to the position that biblical Canaanites are almost entirely fictitious, invented as a foil to the up-and-coming Israelites. Since I do not share his evaluation of the authorship of the OT material (I'm comfortable saying some parts could be exilic or later, but that most goes back to the 2nd millennium, whether in writing or in oral record), I did not find Lemche's study useful. I found many of his explanations convoluted and unconvincing -- and mostly unnecessary, if you simply take even a more moderately critical stance on authorship and date.
This is the first book I have read by this author, and I admit it was the wrong one for my interests, which are the origins of Israelite ethnicity. If that is what you want to investigate, then Ancient Israel: A New History of Israelite Society is the book for you.