So are you saying that you've never filed taxes in Canada? You don't need to be working fulltime to file a tax return.
If you're not going to submit Option C, then you need to submit a letter explaining why. Read further down on the Document Checklist where they explain this.
Also FYI, you don't need and actually can't have a co-signer for a spousal application
I didn't include an Option C printout with my application, and it was not a problem. I included a letter saying that it was not available because I had not filed my tax return and also stated the reason why. I included T-4 slips for that year, recent pay stub and a letter from my employer to demonstrate that I have income.
I never said it would be a problem if you don't include Option C.
I said if you are not going to include it, then you need to include a letter explaining why. That's what you did and what I did as well.