While looking for the postal abbreviation for the US state of Maine (it’s ME, so you don’t have to look!), I came across this chart from the United States Postal Service Historian that shows the different state abbreviations they’ve used since 1831. It wasn’t until 1963 that the USPS settled on the two letter system still in use today, and which we also use in Canada.
One interesting tidbit from that chart is this note about the abbreviation NB:
…in 1969, at the request of the Canadian postal administration, the abbreviation for Nebraska, originally NB, was changed to NE, to avoid confusion with New Brunswick in Canada.
My knowledge of Canada-US relations is not deep enough to know how often the United States has bent to our will (I suspect not often at all), but this certainly was a nice gesture.