CGVD2013 height - EPSG:6647

WKT

VERTCS["CGVD2013_height", 
	VDATUM["Canadian_Geodetic_Vertical_Datum_of_2013"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["CGVD2013_height", 
	VDATUM["Canadian_Geodetic_Vertical_Datum_of_2013"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "6647"]]

Data from @esri/proj-codes

{
  "wkid": 6647,
  "latestWkid": 6647,
  "macro": "PE_VCS_CGVD2013_HT",
  "name": "CGVD2013_height",
  "wkt": "VERTCS[\"CGVD2013_height\",VDATUM[\"Canadian_Geodetic_Vertical_Datum_of_2013\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"CGVD2013_height\",VDATUM[\"Canadian_Geodetic_Vertical_Datum_of_2013\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"6647\"]]",
  "description": "CGVD2013 height",
  "authority": "EPSG",
  "version": "8.3.3(10.3.1)",
  "deprecated": "no",
  "areaname": "Canada",
  "extent": {
    "slat": 38.21,
    "nlat": 86.46,
    "llon": -141.01,
    "rlon": -40.73
  }
}