If I canould choose, themy answer is definitely the countryside.

If I can choose, the/my answer is definitely the countryside.

I agree with the first corrector’s comment.

Suggestions:
• If I could choose, my answer would definitely be the countryside.
• Given a choice, I would opt for the countryside.

I hope I can work remote / remotely one day, then I can move to a village by a mountain.

I prefer “remotely” in this context.

If I canould choose, the answer iswould definitely be the countryside.

What you wrote is not technically wrong, but to a native speaker it would feel a little awkward. Since this is a hypothetical question, it makes more sense to use "could" and "would be" since that tense is more associated with hypotheticals--can and is are more definite.