Interesting, I thought that was a PNW (OR/WA/BC) thing (I've heard it described as the "Northwest vowel shift")? I say "bag" and "lag" rhyming with "vague" or "bagel" too, and I grew up in Oregon.
Manitobans are the worst offfenders on the "bag"/"bayg" meter. If anything, it's the trademark of their accent. It isn't until I point it out do they hear it. anything that Americans (californians especially) say with the short A sound that ends with a hard consonant is liable to be mangled by a manitoban. If you aren't hearing it, it's because your accent is getting in the way (the one you probably swear you don't have).
Ontario residents mangle their A sounds a little different. when you have an "ar" combination in a word, they pronounce it like "air", but as if you're simultaneously having a mild stroke. "Marnie had an Enlarged Heart" is always fun to hear one say.
I have a lot of relatives in the Midwestern U.S. (specifically Minnesota), and you encounter that pronunciation in that region. I have no idea if it spills over into Manitoba or Ontario, but if it does, the location seems right for it.