canada
Case law is limited, but has taken the view that attempted manslaughter is not possible
This has not been decided by the Supreme Court of Canada, but a court of appeal has said it is not possible. See R. v. Menard (1960), 130 C.C.C. 242 (Q.C.C.A.), leave to appeal to Supreme Court of Canada refused:
I find it impossible to conceive of attempted manslaughter; the French translation expresses my idea even better: how can one suppose that a person can mean to commit involuntary homicide?
While the Criminal Code allows for a provocation defence to reduce an offence of murder to one of manslaughter, one court has said it does not operate to reduce a charge of attempted murder to one of attempted manslaughter (R. v. Campbell (1977), 38 C.C.C. (2d) 6 (Ont. C.A.)).
new-york
The Court of Appeals of the State of New York has also accepted that:
An attempt to commit manslaughter is apparently a contradiction because the specific crime of manslaughter involves no intent and accordingly, an intention to commit a crime whose distinguishing element is lack of intent is logically repugnant.
People v. Foster, 19 N.Y.2d 150 (N.Y. 1967), quoting from People v. Brown, 21 A.D.2d 738 (N.Y. App. Div. 1964)
However, in Foster, the Court allowed a plea to attempted manslaughter to stand, in the circumstance where the charge was for attempted murder.
While there may be question whether a plea to attempted manslaughter is technically and logically consistent, such a plea should be sustained on the ground that it was sought by defendant and freely taken as part of a bargain which was struck for the defendant's benefit.
The logic
In these jurisdictions, an attempt requires intention to complete the entire actus reus of the offence. One of the elements of manslaughter's actus reus is the death of the victim. An attempted manslaughter therefore would require an intent to cause the death of the victim. But of course this intention to cause the death makes the crime no longer manslaughter in these jurisdictions, so therein lies the logical contradiction.