On a camping holiday recently, using my 5D Mk IV, I copied (in-camera) all the CR2's from the CF Card in Slot 1 to the SD Card in Slot 2 (as CR2's).
I then inserted the SD Card into the Apple Lightning to SD Card Camera Reader/Adapter, plugged this into my iPad Pro 10.5" and it took 4 or 5 minutes to upload some 200 CR2 Files.
These CR2s appeared in the Apple Photo App in an Album (tagged as CR2's) and I could browse them on the iPad at a high resolution (pinch to zoom in), but I suspect that these were JPG views. When I tried to send one of these via e-mail, the attachment in the e-mail was an Icon with a CR2 filename and the e-mail could not render the CR2 into an image.
I have LR Mobile on the iPad and I was able to open the CR2 in LR Mobile, (from its Photos location) edit the file and save it as a JPG.
This was just a playing around session (executed 2 or 3 times over the week) whilst making a cup of tea, not an established work flow, so I cannot comment on how robust or useful this process might be to a serious user who wants to do some heavy editing.
Cheers
Dennis