I have the Pro-10, so this is most likely close to your issue, and I print from Photos occasionally. A few questions.
Most importantly, if you have 8x10 size paper selected, is that what you are really using? If you're using standard letter-sized, you aren't going to get true 8x10s, as that is sized 8.5x11. (While 8x10 inkjet paper is available, it is not very commonly available) If you are using letter-sized paper, it is going to be a little different..
Have you selected "borderless" on the set-up menu?
Do you then select "fit" or "8x10"? Both will give you some border if you are using letter-sized paper.
Is the print you are trying to make the proper aspect ratio (i.e. 4x5) and you have letter paper - it just won't work and you'll get white borders.
If you are using the most common of the sensor sizes, you are *not* going to get a true 8x10 no matter how hard you try (8x10 is 4x5 ratio, (most) APC (or "crop" sensors) are 2x3 ratio - as are the so-called full frame sensors, and MF4thirds are, well, 3x4 ratio). NONE are 8x10 ratio.
If you tell the machine you are using 8x10 and you are using letter size it may or may not work. (I frequently use the 10x12 size option to print 5x7s on 12x12 specialized paper. It comes out perfectly centered. Who knows why, but I like to experiment a lot. Thats how I discovered the Pro-10, while stating it is a 13x19 printer, can can output bordered 14x25x)
I don't know if this addresses your problem. If it does, great. If not, I would call Canon Support. I have had great luck with them. (sorry, I don't have the number offhand, but
https://support.usa.canon.com should get you started.
(BTW, if you want true 8x10 paper,
http://redrivercatalog.com is an excellent source, and for a lot more than just paper)