Creating a PDF from your Canva file for Amazon KDP is easy! Just follow these steps:
Click Share in the upper-right corner.
Under File type select PDF Print.
Check the box for Flatten PDF (do not check Crop marks and bleed or Include notes)
Under Select pages choose All pages.
Under Color Profile, if you have Canva Pro, then select CMYK. If you don't have Canva Pro, then you can select RGB and most likely, your book will turn out fine. Wait until you get your printed book and if you don't like the colors, then you can consider upgrading to Pro and exporting as CMYK.