I assume because you posted here you are doing an Inland application for PR under the Family Class? If so, make sure to keep your visitor visa status current until you submit your PR application.
Then, when you submit your PR application include an application for an Open Work Permit. Make sure that you mark it clearly that it is not to be processed until AIP is reached (Approval in Principle). What this does is give you "implied status" - this means your status was still current when you submitted an application and you are waiting for a response from them so it is "implied" that your status is still correct until they give you an answer on your Open Work Permit. Once you have the Open Work Permit you don't need to worry about extending your visitor visa.
(This is the same even when applying for a tourist visa extension and you haven't put in for PR - as long as you submit the application before your current visa expires you will have implied status).