Jai Sri Krishna!
Unfortunately, there is not much information in English about Sri Vallabhacharya's Shuddha-advaita Brahmavada online. Unless you can read Hindi or Gujarati, it is quite difficult.
I would
recommend Shyamdas's books; however, since his passing this year, the publishers for his books have not continued his publications, it seems. He is probably the best in accessing Pushtimarg by a native English speaker, as well as a practitioner. His book, "The Path of Grace" is sold out, and would have been the best resource on a preliminary study of the philosophy!
All you're left online for free, would be things in terrible English.
Try these two websites:
shreevallabh.com: Pushtimarg
PhD Thesis on Brahmavad by Shri RaghuNathLalji
Thus, to answer your question in my own elementary understanding:
According to Sri Vallabhacharya, maya in itself as well as the world (prakriti) is not an illusion, but rather another aspect of the Absolute Reality, the Beautiful Absolute, Sri Krishna. However, because God desires to manifest His divine Lila (Pastime, or Play), He manifests all souls (jivas) in three different categories (pushti, maryada, and pravaha), or the souls of grace, the restricted souls, and the moving souls. The first has a tendency towards God, the second has the tendency towards economic growth and liberation, and the third has tendencies toward negativities.
However, all of these souls consist of the Lila of God, and thus ultimately merge with Him. Both God and the souls are Sat, Chit, and Ananda. However, maya is merely a manifestation of God, even if troubling at times.
Just like gold may have one side pure, and the other side with scratches, Vishnu is Supreme Reality, and its temporary manifestations. Unlike Vishishtadvaita, where maya is seen as due to one's ignorance of our divine origin as pure souls, Shuddhadvaitins see maya as a mere aspect of the Divine Absolute's desire (and nature) to manifest His Lila.
If you go to
e-Haveli of Shri-Nathji ! and read under Pushti Philosophy, the essays therein may be of help to you, and contain some information about Shuddhadvaita.
I wish I could help you more in detail, but I was taught under a different Vaishnava school. But if there is anything basic that I could assist you in, let me know!
Good luck!
Sri Krishna Sharanam Mama!