You know my friends work permit expired, but his sponsorship was passed with work permit application before it did, he had to go get police clearance before AIP and was referred to CBSA or CIC office and he was fine, he even talked to a CBSA officer. This just means he was on implied status. He has AIP now and an open work permit. The visitor visa is just easier I guess because you have a valid document with you, but its up to you. It is not a requirement.