Disclaimer: I've pretty much stopped printing photos at home and just take them to Walmart/Walgreens/etc so I'm a bit out of my depth here.
I'm also asking myself, is this more of a KDE Plasma printing issue or an application printing issue?
Possibly a driver issue. Are you using a CUPS driver or does Canon provide a Linux driver for the printer? In order to get the duplexer to work on my laser printer, I had to install Brother's official Linux driver. Maybe 'borderless' is a feature specific to the official driver?
You might try installing the Canon software in WINE and seeing:
- If you can print from that (not sure if it can or not)
- If you can't print directly from that, can the result be exported/saved to a format you can print from Linux? If so, does that addres the border issue?
Beyond that, I'm at a bit of a loss as I haven't done home photo printing in ages. When I did, I just dealt with the borders with a paper cutter.