に - Is a direct particle in the case of direction. You are going TO the restroom. へ - Is more like you're headed to where ever. You are going TOWARDS the restroom. In the sentence you provided there really is no difference. There definitely is a pattern between natives and what they will use に and へ for. Why the difference? Lets say you are headed somewhere but you might stop at different places along the way, or perhaps you may not even ultimately reach your intended destination. へ would be used. What if someone asked you where someone went, but you don't know where they were exactly headed, but you know the direction they went. You can use へ for that as well. Hope this clears things up a little bit.

Hey, Jokin. I'm not a expert, so this is my personal opinion. I think they have the same meaning, too. But, 「～へ行く」sounds more formal to me than 「～に行く」. Personally, I usually use 「～に行く」in daily conversation. But when I want to speak more politely, I tend to choose to use 「～へ行く」. Also, I think 「～へ行く」is more literary rather than colloquial. I feel like I see 「～へ行く」more often in written form. I hope it will help. :)

I would like to answer your question. In this case these sentences are same meaning. You can choose whichever you like.