Yes, Minister!

Why is a Canadian Prime Minister a 總理 (zǒnglǐ), but from the UK he’s a 首相 (shǒuxiàng). Canada and the UK are quite similar politically - they both have Westminster-style parliamentary systems. So what gives?

just to add, the aussie PM is also referred to as a 總理 (zǒnglǐ), also a Westminster-style parliamentary system… in Japanese they are referred to as 首相 fyi…

The reasons are historical. 首相 is typically applied to the head of gov’t (e.g. PM) in monarchies. Constitutional monarchies is a grey area as the monarch is mostly a figurehead. 總理 is a 20th century construct and has been applied to newer countries while 首相 has been retained for the PM of the UK since China’s dealing with England goes back much longer. However, 首相 is also used for Canada, Australia, NZ, etc., just much less often. In constitutional monarchies, 首相 and 總理 can be considered interchangeable.