Alpine maps is very open from memory. Anyone that can’t manage eco and military at the same time is going to struggle against Hardest there.
Early aggression with the flanks, pocket providing castle/imp support to the weaker side is often the play in 3v3.
Siege rams with ranged support in early imp is absolutely brutal. With Engineers too it’s 600 wood, 1700 food and 2min to FU a Siege ram, they will eat an enemy base in seconds.
Civs won’t matter a great deal if you play the right way in 3v3. Massive generalisation, but the truth.