ClioPam

Thank-you both for your replies, I realised i  had not "Resized Document" to 5" x 7" and > saved as  before printing. And alas now the green dots inside print-preview box has disappeared     and down to a white border on just one side.  I think i better had immerse myself in reading the ip8750 manual thank-you for providing the Canon link, homework it is then.
Best get the up to date driver too   When ready to add the download, do i just tick "adding software"  and don't have to tick all the boxes eg. My Garden. Is it like starting from square one all over again getting the latest driver ?  Do you have to go through the long, nail biting  scarey process of reconnecting  your printer to get it online again ?

canon ip8750 site:forum.affinity.serif.com  

Hi @ClioPam,
You should be able to make screengrabs of your PC or Laptop screen which you can then hopefully upload to the forum as either PNG or JPEG files. That would perhaps allow us to see a little bit better the problem you're experiencing in the Print Preview window...
Thanks for confirming, that is good to know...
I basically downloaded a manual from Canon's website here...
https://www.canon.co.uk/support/consumer/products/printers/pixma/ip-series/pixma-ip8750.html?type=manuals
This downloads the manual for the ip8700 series and says the following in relation to borderless printing, though it sounds as though the information is factually incorrect as you've clearly had no issues printing borderless 5" x 7" and 6" x 4" prints previously...
Page 30
If you select plain paper as media type or if you select B5/A5-size as paper size, the print data is printed with border even when you select the borderless print setting. Page 77
Borderless Printing is not available for legal, A5, B5, or B4 sized paper, envelopes, or non-Canon genuine art paper. Page 235
When a page size that cannot be used for borderless printing is selected, the size is automatically changed to the valid page sizes for borderless printing.
  When Other Fine Art Paper, Envelope, High Resolution Paper or T-Shirt Transfers is selected from the Media Type list on the Main tab, you cannot perform borderless printing.
  When the ratio of the height to the width differs from the image data, a portion of the image may not be printed depending on the size of the media used. In this case, crop the image data with an application software according to the paper size.
  Setting a large amount of extension allows you to perform borderless printing with no problems. However, the portion of the document extending off the paper range will not be printed and for this reason, the subjects around the perimeter of a photo may not be printed.  

Not all apps do, or can handle all printer paper formats, the right way. For making borderless image prints on photo paperI often use an older by Canon printers accompanied Canon print utility (named Canon Easy-PhotoPrint EX) available for Win/Mac which always does a flawless job here for selected images and different paper formats.
Here as an example setup for borderless 13 x 18 cm printing ...


 
Now where I write this, I recall that some other forum user some time ago had similar problems also with a Canon ip8750 printer (a forum search might show that older related thread).

From what I have read in the forums, it seems that there are many different models of Canon & perhaps other brands of printers that will do borderless printing only for certain paper sizes, but the additional "non-canon genuine art paper" limitation seems like an odd one.
Perhaps this has something to do with ink spilling/leaking into other parts of the mechanism?

Hi @ClioPam,
Thanks for providing your printer details...
I note from your screengrab that the print you're making is 5" x 7" (13 x 18 cm). The manual states the following:
Borderless Printing is not available for legal, A5, B5, or B4 sized paper, envelopes, or non-canon genuine art paper. A 5" x 7" print is smaller than A5 so I suspect the green dotted lines are therefore a literal indication showing where the white borders are going to appear on the print.
The way I print borderless prints which are too small for my printer to handle is to make the print slightly larger and then include bleed and crop marks which for my printer can be set in the print driver, print on an A4 sheet of paper and trim the print afterwards or if printing two A5 prints, I put two up on an A4 sheet, print borderless and then trim across the centre of the page.