The nearest charter boat services to Cannon Beach would be in Garibaldi, south of Cannon Beach, or to the north, in Astoria or Ilwaco. Some charter services specifically offer burial at sea charters, including Garibaldi Charters and Pacific Salmon Charters.
It should be noted that Haystack Rock is at the edge of the shoreline and, to be legal, ashes must be scattered at least three nautical miles from land, according to The Clean Water Act. The EPA does not permit scattering remains along the shoreline. All burials or scatterings must also be reported to the EPA in writing within 30 days. You can read more and find the reporting form on the Environmental Protection Agency website.