Americans seem to get quite confused if you’re spelling something and pronounce it “zed”.
To be honest, neither is wrong, really. One is older, and one has been adapted over the years.
The pronunciation of “zed” by Commonwealth countries is closer to the letter’s origins, sounding more like the Greek letter, Zeta. In fact, most languages around the world use some form of Zeta or Zed (French: zède; German: zet; Spanish: zeta).
Many Americans don’t even know that the last letter of the alphabet is pronounced any differently beyond their borders!
So today’s question should not be “Why do Canadians pronounce it as ‘zed’?”, but rather “Why do Americans pronounce it as ‘zee’?”.
It’s widely suspected that it is as simple as ‘zee’ rhyming with the majority of the other letters ‘tee’, ewe, ‘vee’, double-ewe, ex, why, and ‘zee’.
Later when the Alphabet Song was created, it even made more sense to rhyme the last letter with many of the others!
But – if you’d like to know, I (a Canadian) pronounce the letter ‘zed’ when I’m spelling something. But I pronounce this challenge as the “Ay to Zee Challenge” and I don’t call Jay-Z, Jay-Zed!