All of the Canadian youtubers that I watch pronounce the letter z as “zi”, as is done in the United States. However, I have read online that it is more common for Canadians to pronounce it as “zed”, as is done in the United Kingdom. Is this a regional thing? How do you pronounce the letter z?


Technically it is. The Japanese pronunciation would say “Zetto” as a close approximation of “Zed”.
But the English dub was done for a US audience (despite the fact that the original English dub was recorded in Canada), so they deferred to the American pronunciation of Z.
This could also be the reason Canadian YouTubers would say zee - why alienate 90% of your market, and Canadians are still used to hearing it from American media.
I doubt it’s any fear of alienating them.
It is likely more the result of those youtubers growing up immersed in American media exports.
TIL