Adult humans of sound mind should be able to end their life when they want to. Professionals should be able to assist them.
And defining that is in no way a can of worms, perish the thought.
it isn't, except by people whose purpose is to confuse the issue. We have no problem declaring people of sound mind before they sign other contracts, the only reason this would be any different is because people against euthanasia would force it to be.
Even if you take a maximally libertarian position on assisted suicide and think that Canada should do the same, the current piecemeal expansion of the practice should still be unnerving because it then becomes a story that the Canadian government is telling about who they think will be missed the least.