Multiple relative clauses within subject?

I'm wondering what is the actual subject in this sentence:
"One of the countries she has visited that I have not is Canada."

To me, everything up until 'is' seems like the subject, but I can't find any information about relative clauses being found in a subject, other than in the case of a 'that' clause that comes first (e.g. That she should forget me so quickly was rather a shock).

If anyone could parse this sentence for me, I would greatly appreciate it! Thanks for your time.

Answer

Break the sentence apart by removing prepositions and supporting phrases.

One of the countries she has visited that I have not is Canada.

Then:

One of the countries she has visited is Canada.

Then:

One of the countries is Canada.

Then:

One is Canada.

Ta-da! The subject is technically "one". That's not terribly useful to an actual person, though, so you could say that the subject is "one [of the countries]".