Can I use my Canonical/Ubuntu.com or Launchpad account to post and / or answer questions here as well?
I use the same name on Launchpad.
Yes you can. The whole network of StackExchange sites supports OpenID logins and since Launchpad provides OpenID login facility, you can use it to register an account here.
After following the Login link, you have the possibility to select an Open ID provider. Launchpad is one of them. Simply press the Launchpad button, enter your Launchpad username and hit Sign In.