Yes, it is legal to use a VPN to play at PokerStars if online poker is allowed in your country. However, keep in mind that VPN usage doesn't make an illegal activity into a legal one. So, if you live in a region where gambling is extremely frowned upon, you might still get into trouble.

You can play PokerStars for real money in dozens of countries around the world, including Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Germany, Hungary, Ireland, Latvia, Lithuania, Malta, Poland, and Sweden, among others.

The PokerStars website is available in the United States, but only players in a handful of states can access the real money games listed there. This isn't because PokerStars doesn't want you at the tables. The poker site is active in almost all the US states that have legalized online poker.