OK, I was wrong about .CR3 not being supported on iPad. It’s an app issue. Apparently, for Canon one must use the Canon Camera Connect app to connect to the camera via WiFi. I tried it and it works. I uploaded .CR3’s with the Canon app, exported them to the Photos app, and from there I imported them into Lightroom for iPad, which was my objective in the first place. This is a needlessly complicated process. I don’t know who needs to fix this—Apple or Adobe—but it does need fixing, IMO. As things stand, this involved process isn’t of much help to me, as I would like to be shooting with another card while my pics upload to iPad Pro from the previous card. Works with .jpg and .CR2, but not with .CR3’s.
Perhaps the import process will be streamlined when Photoshop for iPad Pro is released. For now, my problem is as “solved” as it can be.