(I am using High Sierra 10.13.6 on a mid-2011 2.3 i5 8-gig ram mac mini)
When I try to print from Photos to my Canon Pro-10, the only option for paper size seems to be Tabloid (11x17), and if I put any other smaller size paper into the printer, all I get is that portion of the photo that would be in the upper left of the photo if it had been 11x17. It does not matter if I choose any other size in the print dialog, nor even if I use "untitled". (To be honest, I didn't try anything larger than 5x7 or 8x10 - I'm tired of wasting paper.)
If I use my Canon MX922, I get the size requested (up to its limit of letter size).
I have absolutely no issues with any standard or custom print size if I use LightRoom (up to and including 14x22 on a 13x19 printer). This problem only started in November, and I had only used the printer sporadically since May or so.
(I posted this in Apple Communities. No response. I haven't tried direct contact with Apple yet.)
Are you using Canon's application - Studio Pro? That application is really the only way to go in my opinion. Canon's technical support is second only to Apple Care: 1-800-OK-CANON (1-800-652-2666)
Monday-Friday 8:00 am to 8:00 pm ET
excluding holidays
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