I recently did the Canadian Aviation Document renewal. (An uncomplicated PPL, FWIW.)
Submitted Jan 28 using the app, got email same day (I think) confirming the submission, got email the next day saying it was approved, got the Aviation Document in the mail Feb 9, under 2 weeks later.
Stunningly fast by Transport Canada standards, when historically one is used to months and months of waiting for anything.
It was interesting that the app just asked for a selfie against a white background; one didn't have to go get an official passport-style photo to mail in.
The selfie was a little fiddly since I didn't have enough plain background wall anywhere, so I had to affix a white sheet onto on a big cabinet, tightly stretched to avoid creases & shadows. Also, for the photo taken with the assistance of my wife (so technically not a selfie), zooming in a fair bit was needed to get my head to fill the oval of the on-screen guide. Otherwise with the normal wide angle of a smart phone camera, at the suggested 3 ft distance, one got too much background (past my taped up sheet!) and not enough "head & shoulders" photo. Photo quality was evidently still fine with some zooming on a modern smart phone.
It was also tricky to fulfill the "no shadows" requirement. I think the software rejected my photos a couple times while using the app, until I got it right. Had to get enough natural light in the room to avoid the problem of room lights casting shadows. So it actually worked better for me, turning off room lights, making the room darker but more evenly lit.
So the whole process would probably would work smoother if one handed one's phone to someone at a passport photo place, with their good lighting and background screen, but one can do the whole process at home.
Hope this helps somebody.