SNAAAKE,
Small world!
The arcade at Atwater (Alexis Nihon Plaza) is still there yes and no. It is about 1/2 or so the size that it used to be and has been moved into a small enclosure at the side of the bar that was next door. The other one on St. Catherine street (Amusement Forum) no longer exists.
There is a positive side at Atwater though.
There is a new entertainment complex where the Montreal Forum was (now called the Pepsi Forum). It houses an AMC movie theater, shops and a place called Jillian's. Jillian's has a restaurant, bar, bowling alley and.... a pretty huge arcade. I would say around 50 or more machines. All the machines are very recent and in excellent working order. Just don't expect to be dropping quarters in them. They all use the new cash-card mechanism and are pretty expensive. 20$ can go VERY quickly.
As for Guy-Concordia, news is not positive. There was one on St. Catherine street next to the McDonalds and another inside the Faubourg St. Catherine. Both are now history.
There is still a (very) small one on St. Catherine street very near that location and the small one on the corner of St. Catherine and Crescent is still there. As far as I know, all of the many arcades east of that location no longer exist.
Should you come? Come for the arcades........ but stay for the women.