I thought I would make one additional post on this subject to wrap things up. I've decided to return my Pixma Pro-1 printer. It really frustrates me because other than my issue with the print sizes this printer was everything I had hoped it would be: well built, easy to use, attractive. Print quality was outstanding. No metamerism, no bronzing, great gamut, accurate color. I experienced no paper handling issues and, unlike cxcpman, I didn't notice any excessive ink use (though, as I've said, I didn't get to print what I wanted to print). It is, in every other way, the printer I have been waiting for since I ran the first of many cleaning cycles on an EPSON printer a decade ago.
Having said all that, as I look around my walls at all the prints I've made previously using a smaller HP B9180 with various papers and canvas, there is not a single print—not ONE—that I would be able to print at the same size on the Pixma Pro-1 with its crippled paper/media type functionality. It seems to me that Canon is trying to protect me from myself, needlessly forcing me to choose between image quality and image size. Why not just warn me that image quality might be compromised with my current driver settings and let me make my own decision? Canon's engineers won't give me that choice so I make the only decision I can: look for a different printer.