When we phoned IRCC they told us NOT to apply for the extension it would not be approved because he has an OWP application in which already is an application to remain in Canada. I have since found out that the IRCC call centre agents do not always give out accurate advice and in hindsight they were wrong and we should have applied for the extension. Makes me so angry as I trusted that when you ring the IRCC that they give out accurate information but this is not the case so beware. You get much more accurate advice on this forum from the experienced forum members.
We paid $255 total. It's broken down into 2 different payments one for $100 (open work permit holder fee) and the other for $155 (work permit fee). You need to pay for both and include the receipt.
The documents we submitted with the OWP section were the required payment receipt, marriage certificate, and passport scans, but we also included an additional information sheet where we explained his visitors status, scans of boarding passes showing latest entry into Canada (to prove visitors status as UK citizens don't need an actual visa to enter), bank statement showing joint account with both names/same address. We included these other documents, which aren't necessary, because the illegibility requirements for the OWP are: that you are residing in Canada with your spouse (so the bank statement proves that), that you have valid status (the boarding passes support the fact that he entered Canada as a visitor although not official proof of status so we included an additional info sheet), and that you have an ongoing PR application in. Because of our country requirements we did not have to do medical or anything else. Oh and we also included the checklist which I don't think you have to.
The most important thing to remember when you send your PR and OWP application in is that even though you send off both in the same package, once it gets there an officer separates the two applications and the OWP forms & documents are sent to another office to be processed. They almost become two separate independent applications. This is a very important fact to be aware of so make sure that you have all of the forms, receipt, supporting documents all together in an easy to see section so they know what documents are part of the OWP. I have read on here many people make the mistake of not including the passport scans or marriage certificate, etc. with the OWP section because they think it's in the PR section anyway. This is wrong. They are two separate applications. You need to include the same copies with the OWP as well. The other most common mistake that is made is that people do not hand sign the form at the end. You must hand sign the bottom.
There are other threads on this forum that are dedicated to the application process or the OWP applications, so you are better suited to research those if you have any other questions.