How does the Arena work?

How does playing in the arena work? It isn’t real time right? But then why does it say “finding opponent?”

Does anyone know how your opponent is picked, whether it being real time or something like finding someone who has already played and then taking their score and making them oppose you?

So, while yes the game advertises it as a "live" system, and you are technically playing against other players, you aren't playing them in real time. You are playing what they call "ghost data", and you aren't directly competing with other players, you're simply playing to see who gets the highest score against "bots" using other players previous game data.

Source (Emphasis mine):

Arena (known as Battlez until 7.5.1) is a player vs. player game mode in Plants vs. Zombies 2 that was introduced in the 6.6.1 update. This mode is unlocked after getting the Map of Space-Time-Ness from Ancient Egypt - Day 1 and obtaining at least six plants.

However, in the same article:

It has been noted that this mode does appear to be lacking a "real" matchmaking feature that pairs you with another player fairly. There have been reports of people that had low-leveled plants to still be paired with a person with max-leveled plants or still high-leveled plants. Players can also be paired against bots that solely calculate their score based on the players.

Some on reddit explains this a bit better:

[...] you can stay in the seed-selection screen as long as you could, and you could fast forward the game, and the fact you could exit to home screen and re-enter or even pause the game [...] So what you're seeing your opponent is what your opponent had done, albeit not instantly but maybe a few minutes or hours ago. You're literally playing against a ghost data of someone else, hence why you're actually playing "alone" during Battlez.

The answer is almost certainly "No". It's been proven that the list of opponents is all taken from a stored list of names within the game client. Check the next time you play; for me on Android the last letter of the name is cut off, but every single "player" I see is on that list. An EA representative tried to claim they replace the name of the actual "Player" with one of these to ensure no abusive names slip through. However if you follow one of the online recommended builds for Arena so you have the best chance of winning, you'll find it's also set to scale so each match is harder than the last, with you normally losing around the second game of the second run. Every week, every time. So at the most charitable interpretation possible, they're sampling a final score from the player base, changing their name to the pre-selected list, then ensuring one at a fixed point is impossible to beat.

More likely, it's not a multiplayer service at all.

Which makes how when the week is getting close to an end, one of the players in the last few hours is suddenly pushing to beat your league ranking. Better spend some gems to keep your place and reward, eh? What's that, out of gems. Why the real money store is just over here...

When I realised this is what they were doing, I stopped playing.