When the "Selected Print Size is larger one page, Do you want prints to span multiple pages?" message comes up (which doesn't make sense, as my print is smaller than 13x19) I had been selecting NO. But when I select Yes, the print sizes to 13 x 17.50, as shown when I pass the cursor over the image.
The printable area of 13 x 19 paper on the Canon drivers that I have is 12.685 x 18.70.
Unless you invoke borderless, that is the largest print that will fit. Look above the preview panel, upper right.
If you want to fill the paper, use FIT TO PAGE.
If you ask for a 13" inch wide print, it will not fit in a 12.685 space.
So Qimage gives you a choice, use more sheets of paper, or fit to page.
Fred