In Vivaldi, middle-click does open the link in a new tab, but leaves it unselected, requiring a second click to raise it (and a sweep of the pointer to the top of the screen). I know I can right-click and select "Open in new tab", but that's a two-click solution too.
Hmm, seems like a strange oversight. One would assume that that was a basic feature. Anyway, I combed through the settings in Vivaldi 1.7 and by default there's a mouse gesture to open a link in a new tab (instead of a "background tab"). Place the mouse cursor over the link, press the "right mouse button" and hold it while moving the mouse down, then release. Mouse gestures have to be enabled, of course.