Hey Lauryo,
welcome to the forum!
-proofs of intent to move back can be different things: letters from family proving that they know about your intention to move to Canada, quote from a moving company about shipping your belonging, proofs that you have a canadian account, if you already know that you will stay with family when you arrive, then get a letter from them saying that they are willing to host you... if you start looking for jobs in Canada, or start exchanging emails with possible employers, add that too. You can also make a "timeline" explaining the steps in South Korea that you will need to take in order to leave the country ( rent contract to cancel, notice at your work etc) - to show that you have thought about moving back and you are aware of what it entails, and you are serious about it.
-because you're outside of Canada, you probably don't have an Option C. Follow the guideline for outland, and provide a letter from your employer, as well as pay stubs from your current employer, and explain to CIC what type of job you will get and how you plan to support yourself once back in Canada. What CIC is trying to assess is if there is a risk that you might go on welfare with your family. So just make sure that you show that you have a plan. If somebody will host you when you arrive until you're back on your feet, then get a letter from them stating that.
- how long - that's a good question!
it depends on your case, if it's straightforward ( both first marriage, no kids from previous relationship and a complete application with all documents) it will go faster. Stage 1 is currently listed as 55 days, but a lot of people get done in 20 to 25 days, so it can be faster. After that, your file will go to Manila (as Seoul is closing), and listed is 12 months, but that's the time it takes to complete 80% of the applications - so quite a few people get done before that. I would say plan for 12 months now (stage 1 + stage 2) but there is a good chance that you will be done before.
-no. Once you get the COPR ( confirmation of PR), there is an expiry date on it. It's usually 12 months from when the medicals were done ( so make sure that you do the medicals just before sending off the application), or expiry of the passport if it comes first. that's the timeline to land, and it can not be extended. However, what you could do is: have your spouse fly to Canada to land within the allotted time, and then turn back and go to Korea. Pack, say good bye, and then move to Canada later. She has to live in Canada 2 years out of 5 to maintain her PR status, so as long as you respect that, it's OK. It gives you ample time to turn around and close things in Korea before moving.
Good luck,
Sweden