With my new Steem Monsters "cheating" tool, you can view what cards your opponent submits, before you submit. This takes advantage of this setting, disabled by default:
So far, AFAIK there has been no way to take advantage of this toggle, and peak at the cards of your opponent. That is, until today. Start a SM battle, go to https://smcheat.smitop.com/, enter in your opponent's username (without the @), hit the button, and you'll see their cards as soon as they hit "Submit", instead of once the battle starts.
Keep in mind that it could take a few seconds to load, and once the battle starts, it'll go back to waiting for a team.