For citizens abroad would be sure to submit more concrete proof during processing that you will be relocating to Canada when your spouse gets PR. Things like giving notice to your employer, finding a job in Canada, proof of looking or securing a home in Canada, etc. Lots of posts with couples needing to post more proof of relocation.
we are in the same boat as I live with my spouse overseas. Its kind of hard to give concrete proof like giving notice, mainly because the processing times are so long and varied, based on the local law here in the UAE, we would both be jobless(and our local residency visas cancelled) in 1 month of giving notice of intent to leave our jobs.
Also, how would you apply for positions in canada if you cannot give your employer a date of arrival/no current residency status of the P.A.
From most of what I have read, a letter with a sufficient explanation of a fairly thought of plan is sufficient.
for us, we mainly mentioned that we already own a house in canada and how we plan to live off different sources of passive income until we land on our feet in canada once we do move.