The accents in north america are split east-west, not north-south. I'm from Vancouver but whenever I am in the eastern US they think I'm from california because I don't sound have the ontario/maritime accent they recognize as "canadian". "aboot" doesn’t exist in the west. Never has.
I'm from the Maritimes and have never heard anyone here i know say aboot I think to certain people in the US it just sounds that way. I knew a girl from Liverpool England and she thought I was from Ireland, not 100% convinced but more so than Canada. I'm from PEI which at one point was going to be called New Ireland.
IMHO: We don't say "Aboot", but something closer to (but not quite) "Abehwt", compared to the American "Abowt". From what I can tell, Americans can hear a difference, and frankly we Canadians can't at all. But Americans seem to hear the difference as more exaggerated into the "Aboot" territory.
In short: We do say "About" very differently, and we're generally totally unaware of it.