Vivaldi team has added Chromecast support to latest Vivaldi snapshot 1.5.648.6 and is available to download for Windows and Linux platforms. After installing this snapshot, you can see Cast menu item on right click menu, you can use it to cast a tab to casting devices.
Note: We’ve noticed selecting cast menu item in the snapshot has triggered security alert from Windows Firewall saying some features of Vivaldi app have been blocked, if you face this issue, click on ‘Allow Access’ to use the casting feature in Vivaldi browser.
We were not able to install Google Cast extension on Vivaldi browser, which makes it easier to cast a tab from Vivaldi browser.
You can download Vivaldi 1.5.648.6 snapshot from here.