If you apply inland, you should send the visit visa extension along with your application package so you don't get out of status in case your processing takes a bit longer.
For the open work permit, use the change of status form for a temporary worker. You can find that here: http://www.cic.gc.ca/english/information/applications/extend-worker.asp If you send it with your application package, you can get your open work permit as soon as you get 1st stage approval. If you don't, you have to wait until you get 1st stage approval and then apply for the open work permit.