How to print an oversize document.

Is anyone familiar with the ins and outs of Canon printing software?

I am having trouble printing a 14 x 22 Photoshop document on my Canon Pixma MP620 printer. I want to find a setting that will print out the document on multiple sheets of 8 1/2 x 11 paper (the largest size the printer accommodates) at the actual size - 14 x 22. In Printing Properties > Page Setup > Page Layout, I find a choice called Poster Print. But when I tried this the printer produced an arbitrarily chosen over-sized version, or would have, had I not canceled, which looks like it was going to be about 30" wide, not 14". How do I get the actual 14 x 22 size to print?