Is "Metro" British English or American English?
If you're talking about the underground train system, then I don't think it's called the Metro in the USA and it's only called the Metro in a couple of cities in the UK. The London system is called "London Underground" or, informally, "the Tube".
The system in most of western Europe (France, Spain, Italy etc) is called the Metro.
There is a free daily newspaper in the UK called "Metro".
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Would you use Metro in AmE and Canadian English for the systems in places like France?
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.