The most finicky cultural distinction
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.)

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:
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.