There are absolutely endless possibilities for biking in that region. I don't know many of the on road routes but there are so many passes with stunning scenery that you can't go wrong. You can also just ride around the Engadine valley, checking out the lakes down towards Maloja pass, or head up towards Bernina pass and get a great view of Mortaratcsch (spelling!) Glacier.

If you are looking for off road routes there I can give you more specifics, there really is some of the best mountain biking I have ever discovered in that region.