How to print 4.25"x7.5"

I have been trying to print a book in the same size as the massproduced paperbacks (4.25" x 7.5"), but can't seem to figure it out.
I have the PDF file to size and used Montax to get the pages in correct order, but can't seem to figure our how to actually print it....
When I try to print on standard paper sizes it seems to defult to that page sise rather than the size of the PDF...? Not sure what I am doing wrong or if it is my printer (Cannon G6020).
Any advice / help?