Here's an article from a couple years ago about the retirement of the original double decker buses used in Victoria BC, then slated for replacement with modern double deckers.
Apparently, those were the first double deckers in North America for public transit use.
After more than 20 years of service, BC Transit's first 10 double-decker buses operating in Greater Victoria will enter retirement in early 2021.
dailyhive.com
I could have sworn there were double deckers in Victoria in the mid 90s, but the article says they didn't enter service until 2000. Must have been early 2000s then when I saw them in Victoria.