Just want to add..
"John" is your first name. And "Doe" is your last name in Canada.
I don't know how names are splited in your home country. Normally if someone has a name "John Smith Doe" in Canada, We would assume that "John" is the first name, "Smith" is the middle name and "Doe" is the last name.
Don't agree.
To my knowledge, there is legally no such thing as a 'middle name' in Canada, only first (given) and last (family) names. If 'Smith Doe' is shown in the last name field, that is the last name; if 'John Smith' is shown in first name, it simply means there is more than one 'first name' (usually called given
names - plural.) So it just depends what has actually been entered on the documents.
That said: there may be differences between provinces, archaic forms, etc. And no-one is denying that we say 'middle name' colloquially all the time, and most people will actually use only of their given names. I also can't say what other jurisdictions do, many do have fields for middle names (esp where middle name is a patronymic or similar).
Canada will put all names that are not 'family names' into the given names field by default (you can often ask to omit or specify which given names, depending on situation though). I believe in many circumstances Canadian insitutions will agree to omit one of the family names IF that's what you use consistently, but YMMV.
BTW recently had reason to review old birth certificates and baptismal certificates for a friend - the friend has like six given names (family traditions and the like). Turns out only two of the given names are on the birth certificate, the baptismal certificates have all the other ones - so it turns out my friend's other names are not official in any meaningful sense except perhaps vis a vis the church.
Of necessity I've massively generalized here when saying 'Canada' when often it's the provinces, and Quebec is often different, no idea there. I'm sure there are lots of cases where this generalization is not exact)