Boa Noite Gustavo, existe varias formas na verdade da quais são elas:

Por evento de processo:

function afterCancelProcess(colleagueId, processId) {

// Script a ser executado para o cancelamento da solicitação; 

}

Por WebService SOAP XML:

MÉTODO: cancelInstance

<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:ws="http://ws.workflow.ecm.technology.totvs.com/">
   <soapenv:Header/>
   <soapenv:Body>
      <ws:cancelInstance>
         <username>?</username>
         <password>?</password>
         <companyId>?</companyId>
         <processInstanceId>?</processInstanceId>
         <userId>?</userId>
         <cancelText>?</cancelText>
      </ws:cancelInstance>
   </soapenv:Body>
</soapenv:Envelope>

Por API: LINK: http://lab.fluig.com/api/resource_WorkflowRest.html

POST /2.0/workflows/cancelInstances

{
  "cancelInstanceList" : [ {
    "processInstanceId" : 12345,
    "replacedId" : "...",
    "cancelText" : "..."
  }, {
    "processInstanceId" : 12345,
    "replacedId" : "...",
    "cancelText" : "..."
  } ],
  "cancelText" : "..."
}