Canadian Raising -- which is what creates the sense in 'Muricans that we're saying aboot -- is actually weakest in the Atlantic region, and particularly with respect to Os. We strongly raise our Is and As, but not our Os. "Out and about" is more likely to be pronounced "oat in a boat" out here.

The phenomenon, more generally, occurs coast-to-coast, though, and originated in the 1800s.

Nowhere in Canada has anyone ever actually said "oot and aboot", though. Americans just have this tendency to hyper-fixate on the subtle difference between raised and unraised vowels, and see the raised vowels as very cutting. They'll go "ow-t and ab-ow-t", or put shingles on their "ruff", particularly in the south, and find the more closed-mouthed form of these vowels alien.

In other words original Scottish dialect of isolated settlements