protect is not changing the source of the damage, it is still coming from an opponents unit. if you character is dealt 3 damage then you can only redirect 2 of it to your guardian because it only has 2 health. 

the rules for protect clearly state that you can't direct more than your remaining health, so if it has 0 damage on it then your max protect damage is 2, you could then prevent 1 with shields. 

TGO said:

The argument is that Protect is an effect controlled by the owner of the card that has it. So damage that is re-assigned via Protect is part of the "controller's effect" and therefore ineligible to be shielded, because shields "cannot prevent damage and focus tokens placed by its controller's costs or effects".

That is an interesting argument. I guess I just don't see it worded that way at all. The source of the damage does not change, it is merely reassigned to a different target instead of its originally intended target.

MasterJediAdam said:

That is all the ability is doing. The ability is not preventing the original damage and creating new damage, just redirectig it. 

TGO said:

Concur

MasterJediAdam said:

I agree with both of you on this, the source of the damage does not change. But it is a "controller's effect" that re-assigns it.

Frankly I think the intent is for shielding to work in this case. I am only playing devil's advocate because I do see how it can be interpreted the other way. Hopefully the FAQ will clear it up soon.