Drupal 7 connection to MS SQLServer/PostgreSQL
Can MySQL handle this amount of data?


Yes, MySQL can theoretically handle many millions of rows (see How many rows in a database are TOO MANY?).

What actually matter are your server resources, configuration, and indexes. If you're not sure about the first two, consult with a professional dba who will be able to help you fine tune your settings for both Drupal, and, more importantly, the specific usage of your app.

Drupal core tables are heavily indexed (as are many tables provided by contrib modules), so it'll probably come down to the custom/contrib modules you have installed from that respect.


  if not Can Drupal 7 connect to MSSQL Server and work with it as good as it works with MySQL? what about PostgreSQL?


Yes, Drupal can use both MSSQL and PostgreSQL. How well any of those perform will entirely depend on the same things mentioned above. I doubt you'd see massive differences in any of them, unless your app is used in a particular way that one or another is better suited for (but the only way to work that out is by benchmarking).