The Dutch giants are preparing a four or five year contract for the 19-year-old, with a fee expected to be between €8m and €10m.
A whole host of Premier League clubs have been linked with the Holland international. A previous winner of the Dutch Talent of the Year award, Maher is regarded as one of his country's best young prospects.
He had stated earlier this year that he'd prefer to remain in the Eredivisie were he to leave AZ, but Ajax - one of the favourites to sign the teenager - pulled out of the race this week.
That opened the door to a Premier League switch, with Chelsea and Arsenal joined by Manchester City and Tottenham Hostpur.
All have scouted the youngster, and a number of Premier League scouts were in attendance to watch the Netherlands under-21 compete in the European Championships in Israel this summer.
Maher won the KNVB Cup with AZ last season, and has already made 66 Eredivisie appearances for his club.
The teenage attacking midfielder was reportedly a target for PSV in the January transfer window, but he now looks set to complete the move six months on.