I can't pretend I do a great deal of sequencing, but used cubase years ago for a bit (well tried to), and then tried cubasis when I bought GPO. However I gave up with it as I could never understand its complexities and got a copy of Sonar LE as I found it cheap on ebay.
I find it much more user friendly that cubase as I like the way the interface is set up - it just seems much more straight forward and easy to navigate. I've thought about upgrading it to full sonar, but for the amount of use I give it I find it does everything I want it to do.
Probably not a lot of help but just my 2 cents worth
Here is an article on (I think) an older version of Sonar LE from Sound on Sound, which should give you a quick overview. If you're running the full version of Cubase (not Cubasis) you have more tools at your disposal. If you're running the version of Cubase that came with older versions of GPO or one of the light versions, you may find the features comparable or even better.
Cubase and Sonar do the same things. Their interfaces, workflows, and commands differ.