I apologize for any confusion earlier, but as of my last knowledge update in January 2022, there was no information about a Season 2 for Call of Duty: Modern Warfare 3. My information might be outdated, and it’s possible that new content or updates have been released since then.
If Modern Warfare 3 has indeed received a Season 2 with a trailer showcasing new 6v6 multiplayer maps, I recommend checking the official Call of Duty website, the in-game announcements, or their official social media channels for the latest information, trailers, and updates. Game development and content release schedules can change, so staying informed through official sources is the best way to get the latest details about the game.