My understanding is after 10 years, with no further issues, you are good to go. I got a "driving award" in 1994 and went into Canada in 2006, 2010, 2012, 2016 with no issues.
I had to get a letter from the court indicating that I had completed everything with my sentence. Mine was also over 10 years old. They still held me up at the border and searched my car, but finally let me in.
It used to be 10 years. I believe they changed it so now they can basically mess with you no matter how long it’s been if they want. I’ve crossed the border several times since my dui, and the only time they messed with me was when it had been a little less than ten years. They said you can either go back or pay a $200 “ temporary residence fee”. I paid it and we were on our way. Haven’t had any issues since. Think it’s been 23 years since my dui now.