2 -correct, bc there is "and" used. It makes verb plural, even if connects singular subjects. If it dificult to comprehend try to reverse the words:

a federal law and a provincial law (is/are).... ?

My choice is A

Where there is a federal law and a provincial law

read this parallel sentence again...where there is a federal law ...where there is a provincial law

OA please

Barron's Official answer is B - which I am against.
Reason why I am against:
Alternate forms where plural verb is applicable.
1) Fed and Prov laws are required in a place for the doctrine to be applicable.

2) Canada should have fed and prov laws for the doctrine to be appicable.
- have is needed for conveying the subjunctive mode and not because fed and prov forms a plural verb

Alternate forms where singular verb is applicable.
3) The doctrine applies in Canada because the country has both fed and prov law.

4) The doctrine applies in Canada where there is fed law and prov law.
"where" modifies "canada". If you were to form a sentence without the modifier where, you will land up in a sentence similar to (3) above.

nasa wrote:Barron's Official answer is B - which I am against.
Reason why I am against:
Alternate forms where plural verb is applicable.
1) Fed and Prov laws are required in a place for the doctrine to be applicable.

2) Canada should have fed and prov laws for the doctrine to be appicable.
- have is needed for conveying the subjunctive mode and not because fed and prov forms a plural verb

Alternate forms where singular verb is applicable.
3) The doctrine applies in Canada because the country has both fed and prov law.

4) The doctrine applies in Canada where there is fed law and prov law.
"where" modifies "canada". If you were to form a sentence without the modifier where, you will land up in a sentence similar to (3) above.

Your explanation is confusing (to me) because you seem to talk of 4 sentences whereas your original posting has only 2 sentences. You also write about the subjunctive whereas the sentences you originally posted don't deal with the subjunctive.

As far as your original posting is concerned, SOlaris is 100% correct.

There are a federal law and a provinsial law.

SOlaris wrote:2 -correct, bc there is "and" used. It makes verb plural, even if connects singular subjects. If it dificult to comprehend try to reverse the words:

a federal law and a provincial law (is/are).... ?

2 option is the correct one. If it's confusing try to reverse the order :

The doctrine applies in Canada, where there are a federal law and a provincial law. - federal law and provincial law are in Canada...

Besides, 'and' connecting 2 subjects always requires plural verb form.

Agreed.
To say
"I like shops, where there are books"
is correct than to say
"I like shops, where there is books"

In a similar tone, option B is right