You need to be clear about what you want to happen.
If you would like to be dissected and examined by students then I suggest you contact local universities with medical schools.
If you want to donate organs then this is quite easy in most countries. You either carry a donor card, or fail to carry an opt-out card, depending on the laws applying.
If it is organ donation you have in mind then you should discuss it with your family because what looks dead to a doctor sometimes looks suspiciously alive to a grieving relative. There have been recent advances in taking organs from a clearly dead body and re-using them, but normally the surgeon likes to have organs from a body with a beating heart and working lungs (even if these need the assistance of machines). Unfortunately, when the doctor says, "The patient would die if we turned off the machines", he/she doesn't want to prove it because it might spoil the organs.
Who'd be a doctor?
