Midi keyboard for sonar 7

By Endinol I suspect you meant Edirol.  Those are Roland keyboards.

Most any GM (General Midi) keyboard will work with Sonar as long as it has a midi connection that works with your PC or laptop.  Some have a USB connection.  Some have midi IN and OUT connections which require some kind of midi interface.

Some of the devices are called "controllers" and have no built-in sounds.  Controllers send midi commands to the PC to trigger sounds (software synths) installed in your PC (in your case, in Sonar).

Some of the devices are called "keyboard synths".  They have sounds built-in which can be triggered by sending midi commands from Sonar to the synth.  They also send midi to the PC just like the controllers do so they can trigger synths in Sonar.

Some of the keyboard synths also have built-in speakers so you can play them without a PC.  They might also have auto-accompaniment, recording facilities, etc.....

If you just want to trigger sounds from synths in Sonar, most any cheapie model with midi capabilities found in department or big-box stores will work.  Roland.  Casio.  Yamaha.  Etc.

Serious piano players most likely would want more expensive devices with more keys (up to a full 88), velocity sensitive keys (most will have this these days), and weighted keys (they feel very much like a real piano).

--Larry