If you are not planning on going to the soccer, best to stay away from Cardiff on & around June 3rd, 2017.http://www.visitcardiff.com/uefa-champions-league-final/
this is ridiculous advice
you can point put an event is taking place - no different from rugby matches - but to say don't visit comes across as scaremongering
Massive security is planned with many roads closed. Transport systems will be stretched. Hotels will be fully booked/expensive. If you are not interested in the soccer, it would be prudent to visit on another day.
This is what the local press here saying:>http://www.walesonline.co.uk/news/local-news/full-extraordinary-details-champions-league-12861364
no different from rugby matches
Very different-squared. The event in question is the UEFA Champions League final; the European equivalent of the Super Bowl one of the most watch sporting events in the world. All hotels will be booked solid that weekend, and security will be tight.