I mostly play a 2h dps guardian. It's a lot of fun but as others have said you won't be able to tank much with it. This wasn't always the case but turbine decided to give us more dps at the expense of threat generation and survivability. So don't expect to do full on raids but things like 3 mans or even some 6 man instances you might be able to tank. It will be mostly dependent on who you are grouped with. It is hard to hold agro cause you don't have much taunts when in over power (2hand mode) so you have to hold agro through sheer dps. I've done it a few times and I can tell you it feels quite good to be able to hold agro with just dps as a guard seeing as how we generally have very ###### dps when tanking.You'll need a damn good healer though to keep you alive as turbine has turned our 2h setup into something that uses paper for armor. You'll need some dps'ers in your group that work a little harder at managing their threat. I would figure most pugs won't want you dps'ing and want a "proper" tank...but whatever, just find some friends or a kin that lets you play how you want and you can tank in your style quite a bit. Just not the harder stuff.
Personally I have a glass cannon type build for my 2h setup. I've never gone out specifically to tank with this setup (I hate tanking) but have taken over in an instance or two when I've needed too.