Card-themed heroes and villains are always fun, particularly when you mix and match the various suits to resonate story themes. Black Jack was an MLJ golden oldie with a simple origin: he was a cop that crooks thought they 86'd, turns out he was alive and wanted to beat the odds as the costumed Black Jack. The Jack of Hearts had a more convoluted origin at Marvel Comics, as the hybrid son of a human father and alien mother. Consumed with energy activated by a special fluid, he needed to wear a special suit to contain his power (shades of Human Bomb).
What would make this crossover terrific is by throwing in DC's Royal Flush Gang as the antagonists that are pair of Jacks have to unite to defeat! With the wildcard, Joker, pulling the strings!