If a person is strangled and subsequently embalmed, how would a pathologist determine the cause of death?

Strangulation. A medical examiner would autopsy the body before it is embalmed. In a strangulation case, there would be evidence of a crush injury to the windpipe and probably strangulation marks around the neck.
Easily. Embalming should not be a problem. Like everyone else, a pathologist will look at the history, circumstances, and police report. Unless a person unable to resist at all is smothered with very little force, there will be signs of injury, especially on the neck (strangulation) or mouth (smothering) deep in the tissues. These range from bruising to injury to such structures as the hyoid bone.
Carefully! Autopsy is performed before embalming, and multiple areas of evidence can point to strangulation. Asphyxiation (hypoxia) would be the cause of death; the method strangulation (other causes for hypoxia exist, such as carbon monoxide or drowning). Finger marks (bruises) on neck, broken trachea and/or hyoid bone, scleral petechiae, fibers or dna evidence, even fingerprints can all add up.