Correct Pronunciation

[calvin]

Plough was spelt as I just typed it when I was growing up in Canada. I'm not sure what the official spelling is now, but I never heard that they changed it.

As I wrote, it was Webster who changed it to “plow” in the US. His changes were not generally adopted in Canada, which was a British possession. A few other changes he made in the US:

color for colour, favor for favour, etc [leaving -our for the sound in hour, sour]
center for centre, theater for theatre
mold for mould [like old, bold, cold, ...]
draft for draught [like raft or craft, leaving -aught for the sound in caught, taught]
magic for magick [because "magical" had no "k"]

He is also given credit [or you can blame him if you like] for “jail” instead of “gaol.” Both existed in English but “gaol” was the accepted spelling, Webster went with “jail” [like fail, nail]. It caught on quickly in the US and gradually elsewhere.