Well it seems like the CBSA agents are tired of policing this stuff. I explained to the agent I gave my NEXUS receipt to that I couldn’t upload my fully vaxxed 5-11 year olds QR codes. She explain that it didn’t matter for being randomly selected for testing (which was not my concern), she put a couple of red marks and numbers on the receipt but didn’t specifically say whether or not we were to get tested, and when I handed it to the next agent at the exit, he initially said “go ahead”, but then he said “Oh wait, two kids need to get tested?”. I explained that she hadn’t told me that, and told him about my inability to upload the kids QR codes, and he said ok that’s fine just go through to the left. It looked like a pretty long testing line at the right so I’m glad we didn’t have to do it!
I saw just now that someone on Facebook posted a workaround to upload the kids QR codes: I edited their birth year to 2009. Uploaded the vax record then re-edited the birth year back to the right one. We just came through the border tonight and there was no problem with this.