Juan Guaidó is only the interim President of Venezuela.
He is also a socialist. Not a hard core communist like Maduro, but still a socialist.
Trump showcased Juan Guaidó at the State of the Union primarily to embarrass the democrats and to illustrate the evils of socialism. A secondary goal was to show American support for a regime change in Venezuela. It was brilliant, and it worked.
I don't think that Trump was supporting Juan Guaidó himself, just what he represents.