Gaea's Protector must be blocked if able.
4/27/2018 Only one creature is required to block Gaea’s Protector. Other creatures may also block it, and are free to block other creatures or not block at all.
4/27/2018 The defending player, not you, chooses which creature blocks Gaea’s Protector.
4/27/2018 If each creature the defending player controls can’t block for any reason (such as being tapped), then Gaea’s Protector isn’t blocked. If there’s a cost associated with blocking Gaea’s Protector, the defending player isn’t forced to pay that cost, so it doesn’t have to be blocked in that case either.