According to a recent blog post, those in Ireland, Romania, and the Philippines can all get involved right now.
The third game in the series will be a free-to-play title with IAPs, and it'll be playable entirely in portrait mode. The new 3D visuals look pretty good to my mind, but I will admittedly miss the strong 2D style of the earlier entries
You can also expect a number of gameplay tweaks and refinements, including expanded uses for the sunflower unit.
It's been a fair while since I last played a mainline Plants vs Zombies game, but I've certainly enjoyed the Garden Warfare spinoffs. I might even prefer them to the tower defence originals.
At the time of writing, no firm launch date has been set. A global launch will likely arrive later this year, but for now, only a select few can give this one a go. We'll be sure to let you know as soon as further info appears on Plants vs Zombies 3.