OP had a proposal and question worthy of discussion. This thread went off the rails with some very silly "wouldn't trade McD for Slavin straight up" buffoonery.
It would make the Canes better. McDavid's game-breaking ability would more than compensate for what they would lose off the back end, where they'd remain quite strong.
Slavin would give the Oilers two solid defenders with him and Ekholm. Big improvement. It does nothing for their goaltending woes though.
The Oilers trade their all-world, generational center, who could well end up one of the all-time greats, for two top-quality players, but still leave a gaping hole in their roster. The value is at least debatable, but it just wouldn't make sense for them.