I think if we ever see an alien, he will either fly to us in a completely enormous nuclear rocket which we will spot years before his arrival and deceleration. This is in the case if there is really no other way to traverse stars besides conventional rocketry.

But in case if there is a way to trick any of the fundamental physics we know after all, then very likely the guy will come right at our porch, and they've probably done so many times without us even noticing, and will only contact us, if ever, on their own terms.

Given the premise is right, and somebody can really do something on the level of fundamental physical force manipulation for space travel, then there would be no reason for them to not dispense with conventional space travel altogether, or at least to a reasonable extent where this technology is more practical than giant nuclear rockets.

And the same goes for things like stealth technology, or inertia control. If somebody can arbitrary manipulate gravity, entropy, or fundamental forces to travel stars, or make traversable wormholes, then inertia cancelation, invisibility by directly manipulating light, undetectable radio comms, and power sources unlimited or almost so by heatsink capacity should be child's play for them too.