As a Canadian it really depends whether I say Zee or Zed. Looking online I was surprised to see that it has apparently been Zed in Canada for a long time, but I distinctly recall being raised on Zee until about the mid 2000s then everywhere in the curriculum it was Zed and I started hearing it more. Probably the biggest influence on whether I say Zee or Zed just depends on pop norms, and what sounds better.

Some examples:

• Zee Zee Top, obviously
• Jay Zee
• 350Zed and 370Zed (in reference to Nissan's sportscar models, this actually changed for me over time, for the longest time I would say 350Zee or 370Zee, but when referring to the model broadly, it's always Zee Cars, or for the classic model, it's Fairlady Zee. Fairlady Zed just sounds awful)
• Day-Zee (the movie and video game)
• Dragon Ball Zee (ALWAYS, Dragon Ball Zed would be madness, I've never even considered saying Zed here, perhaps because I encountered it more in my Zee prevalent childhood)
• Zed-DX (the Acura)
• BMW Zed4
• La-Zee-boy (the sofas, obviously, ruins the pun otherwise)
• Alfa Romeo SZed (another car, it seems any time it is separate letters or a series of letter making up a name it's virtually always Zed)
• ABC song, is always Zee for me, but I've heard others say Zed her often. To me it's weird because otherwise it doesn't rhyme with "next time won't you sing with me". Oddly if you asked me to say the alphabet backwards though, my first instinct would also be Zee.
• the phrase "from A to Zee"
• If you asked me what the last letter of the alphabet is, or to spell Zebra, I would say Zee, it seems when referring to the letter alone I pretty consistently use Zee
• I just asked my wife to spell Zebra and she said Zee though

At least the British and Americans are consistent, I don't even know what the heck I'm doing here!