I presume you mean the Canadian eTA?
I got an eTA with a criminal record and was allowed in, no problem. I was economical with the truth when answering the question about convictions.
When you get there, there is almost no human interaction. You go straight to a machine where you scan your passport and fill in a customs declaration. The machine then prints a receipt, which you pass to a border officer, who barely checks your passport and just ushers you through.