The most finicky cultural distinction

Topographical map shows the vast province of Ontario and the Great Lakes region up to Hudson Bay
3D map of Ontario, seen on the tour of Provincial Parliament in Toronto.

This has to at least be a contender. According to the literal Government of Canada:

Typography and punctuation [of e.g. and i.e.]
... A comma is optional after these abbreviations. (Use of a comma is American style; omission of the comma is British style.)
e.g., i.e. – Writing Tips Plus – Writing Tools – Resources of the Language Portal of Canada – Canada.ca
A writing tip on the terms i.e., e.g. and etc.

Honestly, I love the flexibility of not needing a comma! Point for Canada.

On a related note, here's a great database for quick reference on Canada versus U.S. spelling distinctions:

Canadian, British and American Spelling
Canadian, British and American Spelling

What's your favo(u)rite finicky cultural distinction? Here are a few more off the top of my head:

  • Some Canadians do not use the verb "call." Just "phone."
  • Parkade, obviously a top-tier word for parking garage.
  • Pencil crayons are colored pencils. I enjoy that this invites contemplation of what, ultimately, these implements really are in their essence.