The Champions League doesn't really do anything to try and appeal to non-football fans, it's a sporting event pure and simple. A big deal to football fans, but not so much to everybody else.
The Superbowl draws in a lot of non-sport fans through reasons unrelated to the game itself. The hype, the flashy half-time show, even the adverts in between that companies spend millions on. It puts itself across as more of a family orientated thing, and something that will appeal in some way to everyone. Also, considering it's the country's main sport, i'd say it's probably more comparable to the World Cup final as oppose to the CL final, not from our point of view because football is our main sport and the World Cup is obviously a huge deal to us and most of the world, but from their point of view there isn't really anything bigger than the Superbowl.
I do like American football and I watch the Superbowl, but as a football fan first and foremost I prefer the Champions League Final.