The queue is similar to how normal arena (based on observations on meeting people outside my xserver bracket) and bonds. All of the servers in your region is capable of being queued together. Bonds is different as it will match based on various factors such as rank, power, and who is available which happens for me whales - which is a RIP moment. Seems like 3v3 doesn't have any of these factors as me and several others have pointed out that they meet people from older and newer servers and they happen to be running all type of teams ranging from team 7 to edo hiruzen blitz.
You also have to consider that newer servers have players that are still learning to play the game and may have ignored the 3v3 without understanding what it is while older servers than you already went through that process.