In a way you have answered your own question: because you cannot pick "transparent" as a border color, you are selecting white (or accepting the default white) and when using absolute colorimetric intent, white is clearly defined and is almost never the color of the paper.  This is a bit of an odd request because there is almost never a call to print photos in absolute colorimetric intent and even less of a reason to do that and then have a border that is an unspecified (paper) color that doesn't match anything in the print.  But you CAN so what you are asking...

Your request can be done with photo mats since those can be transparent:

• Add your print to the live view at the size of your choosing and then click on the print on the live view to select it
• Now right click on that print and select "Photo Mats (uneven borders)" and then "Add Photo Mat"
• Enter the border sizes on all 4 sides: they can be equal or unequal (your choice)
• Click "Shrink" or "Grow" depending on whether you want the borders to be included in the current size or you want to "grow" the print size by the border amount
• Click "OK" (note, the color of the mat doesn't matter because we delete it in the next step anyway)
• On the live view again, click on the mat/border you just added to select the mat itself (important)
• With the mat selected, look on the bottom of the "Prints" tab where you see "Inner" border
• Highlight the value in "Inner" border and change it to 0 (zero)

You now have a transparent border around your print: it's basically a "spacing" and nothing prints there.  See attached for clarification.

Regards,
Mike

This is unfortunately one of those things where you will find that opinions are a dime-a-dozen.  Your reference is from Canon.  Here's one from Epson:

"Absolute Colorimetric:
This setting renders an image by maintaining an absolute color range so that there is a 1-to-1 ratio of absolute lab coordinates. This setting is not recommended when printing photo data and normal conversions."
https://files.support.epson.com/htmldocs/pro78_/pro78_rf/softw_4.htm

Now my take...  Absolute is the same as relative except that relative adapts all colors to the white point of the paper.  Absolute basically alters the color of the paper (by putting some ink on it) so that the paper essentially becomes the same "white" as the white point of the image (usually D50).  In doing so, all other colors are shifted as well to match the new "paper color".  So the odd part that I was referring to is printing with absolute and then not caring about the border color or that the border color is undefined and won't match anything in the image.  Since handling of the white point is the only difference, printing in absolute colorimetric is not usually a fix for "dark and dull".  If your images look dull and dark in relative colorimetric, you may have other issues that are just masked by using absolute.

Absolute is the most useful when doing proofing under controlled lighting where you are trying to reproduce the output of one device on a different device.  Canon (in your quote) hinted to one of the problems with absolute colorimetric intent.  Because all colors are being shifted to simulate a white point that is different than the white of your paper, some of the printer's gamut is "used" to simulate that shift which necessarily reduces the usable color gamut of the printer/inks you are using.  The other issue with absolute is that you can produce an "absolute" match but if you aren't viewing the results under perfectly controlled and neutral lighting, it still isn't going to be "accurate".

Regards,
Mike

I've tried it on several papers with different profiles.  I wouldn't use it just because of that white crush.  AC basically makes everything from about 240,240,240 to 255,255,255 white.  You're losing a decent amount of range there.  Honestly, I've never seen much of a difference other than AC crushing whites.  As I said, if you are using AC to correct issues where things look dull or dark, you're using the wrong Bandaid.

Mike

Don't use any of the "Template" placement methods with borders or mats.  The templates will conform to the size of the prints but the borders will interfere.  Just use IntelliSpace or IntelliCenter.

Mike

I'm guessing that if you use cut marks that lie on the edge of the transparent mat (like solid line, corner marks, etc.), the mat itself is making the cut marks transparent too.  Try using cut marks that extend outward away from the print: like crop marks or guide lines.

Mike