I just wanted to give an account (and reassurance) of travelling to Canada on holiday, using an eTA.
It was incredibly quick and easy and took less time than returning to the UK!
I did the eTA in advance, which is now mandatory (similar to the ESTA for the US). It was approved in seconds.
When I landed in Canada, I was directed to a machine to fill out a joint immigration/customs declaration, which takes 30 seconds. This is now entirely automated with no human interaction. You scan your passport into the machine and tick "no" to the questions about carrying live animals, firearms, etc. The machine gave me a little bit of paper that looked no different from a shop receipt.
I was then directed to a human who was sitting at an old-style wooden table. No passport machines anywhere. I gave her my passport and the receipt - she glanced at the receipt and passport for 2 seconds, smiled and said "thank you, enjoy your vacation". Not even a passport stamp!
So the customs/immigration process is 100% automated and takes 30 seconds max, while the human visual check takes 2 seconds.
The Canadians really are some of the friendliest people, even their border security staff!