What you will probably find surprising is that the producer of the Gintama live action is a hollywood movie studio named warner bros who in the past have made a few live action from Anime which all ended as failures because of using western cast. It seems warner bros have learned from its previous mistake of using western cast when making Anime live action in the past because the Gintama live action are using Asian cast, warner bros probably want to follow the same success story of the Shingeki No Kyojin live action who become very successful especially in Japan because of one of the reasons is Japanese are using Asian cast.
The most important thing to make a successful Anime live action is by using Asian cast because Anime characters are based on Asians no matter what hair colors, eyes colors, story, etc they have http://antiwesterncosplayers.blogspot.com/2017/01/evidence-racist-westerners-who-claim.html
Gintama Live Action 1st trailer