There have been about three 'Godlike' versions of Solar over the years -- all of which are casual multiversal powers... And a couple of them are Supreme Being-level.
The dude was Molecule Man, before there was Molecule Man.
For a point of reference: the most recent iteration of Solar(who I refer to as 'Solar-Prime') created the entirety of Gold Key/Dynamite Comics --an entire multiverse-- with a stray/subconscious afterthought. What's more, the energy he expended to do this was so insignificant(relative to him, of course) that Solar-Prime didn't even realize he had created an infinite amount of universes at first, lol... And at the end of the story, his power was used to destroy said multiverse just as effortlessly, and compress the whole of Gold Key/Dynamite Comics into a single, unified universe.
On top of all that, Solar-Prime was also explicitly stated to possess both infinite power/omnipotence(obviously), AND infinite knowledge/omniscience. IOW, he is, for all intents and purposes, THE Supreme Being of his company... Entirely responsible for the creation/destruction of Dynamite Comics as a whole, and ALL of the characters within it -- the literal Alpha&Omega.
*Scans to all of the above can be found here, btw.
Anywho, do I think a prepped Constantine can defeat a true Supreme Being-class character? Granted, I know he's one of the most haxx characters in ALL of comics -- but I still have my doubts for obvious reasons.