At bare minimum I suggest "From the Ground Up" which I believe is the standard book used in Canadian FTU. My flight instructor recommended "ASA The Pilot's Manual - Ground School" which I found to be better than From the Ground Up except the law section since it's for US. If you are planning on starting ground school in Canada, don't bother with "From the Ground Up" since they will make you buy a ground school kit which most likely include that book. The ASA book is $60 from Aviation World and $40 from Amazon US.
The Pilot's Manual: Vol 2 Ground School