Camunda is able to import any model that adheres to the BPMN 2.0 standard. It is also able to export models to that standard.
If you manage to export the models from Visio into that format it should be quite easy to transition to camunda. Although in my experience MS-Visio does not export valid BPMN 2.0 so unless there’s some conversion from Visio’s proprietary standard to the open BPMN 2.0 standard migration will likely be a manual process.