Reckless Brute attacks only if it's able to do so as the declare attackers step begins. If, at that time, it's tapped, it's affected by a spell or ability that says it can't attack, then it doesn't attack. If there's a cost associated with having it attack, you're not forced to pay that cost, so it doesn't attack in that case either.

You choose which player or planeswalker Reckless Brute attacks.