Removing spray can paint from engine compartment

Depends on the raffle can. Sem and Martin Senour both make primers that are compatible with auto paint. Probably other pro paints as well. Problem can be lifting, crazing, and other maladies. Base may go on ok if base coat clear coat but react to the clear. I'd be more concerned about how the metal was prepped. If epoxy was sprayed on it if bare metal. And adhesion. If you are willing to gamble do a small area and see what it does. With the work involved to do it over if it was questionable I'd strip it.

If you're lucky, they didn't properly prep before spraying.. A pressure washer might be all you need to peel the new paint off. You'll want to clean the engine compartment of the caked on grease anyway, so it won't be a waste of time if it doesn't remove the paint

As stated, start by pressure washing.  A heat gun might cause the rattle can paint to sluff off the factory paint.  What ever you do, start with the least aggressive and work to the hot stuff.  Paint stripper or walnut blasting are your last choices.

Try lacquer thinner and Goof Off too.  If it was spray lacquer (not likely but possible) you are on easy street.   Joe

Brake fluid will work too good,  it'll take off factory baked enamel if it sets on the paint very long.