I would not tell them you are getting married at this point. It is not about withholding information or lying, it simply makes no difference. The sponsorship/permanent residency application makes no distinction whether you are married or not. They may look slightly more in favor of your application but unfortunately it is the same timeframe, about one year. This means once you submit your application, you will expect to wait about a year for the full approval. We applied in August 2018 after my partner and I were together nearly 2 years. We applied under family sponsorship - conjugal. We had to document extensively proof that we were in this relationship for at least one year. This was submitting emails sent to each other, text messages, dates of visits, photos and 3 letters from those familiar with us about the verity and seriousness of our relationship. All of this went with the application. We received sponsorship approval from Canada in March 2019, seven months after applying. Since my partner lives in Quebec, we then had to apply to Quebec. We received sponsorship in May 2019. I am still waiting on the documents requesting me for the mandatory medical exam. Then it may take an additional 90 days for them to review the exam and provide final approval.
I am not certain about your situation. These forums can only truly be helpful if you provide details of your situation. Of course, we are not talking about birth dates, names, etc. (Trying to keep this light. I know firsthand how stressful it can be). You mention you have a daughter and house back in the states. The Canadian government sees your situation perhaps as a red-flag, hence, only approving your extension by 6 days. They know you can walk away from a house and certainly and sadly, from a child. They see ties as a job, as a primary caretaker, etc. The assumption here is that your daughter is older and on her own. Regardless of her age, you will be providing her details and she will also need to possibly undergo a medical exam as well. In your permanent residency application, you will list any siblings, living parents, ex spouses, common law partners and children. They do this because once you become a resident, you can sponsor any of them (except for your exes, of course! Lol)
Cross the border and don’t panic. When you come back the next day right before your marriage, just say you are visiting with your boyfriend for a few days. Voilà! You are in.
I sense anxiety and frustration in your posts. I understand. Completely. But I would advise applying for all 3 — work permit, sponsorship and permanent residency. Unless you are a highly skilled worker, there is little chance this will get approved. The fees for sponsorship approval for Canada and Quebec, along with permanent residency of Canada, came to well over $1,000. And the paperwork! There is a lot!
Our personal situation led us to postpone our marriage. We have nearly been together now 3 years...that’s 3 years of only seeing each other every 45-60 days, talking on Skype every night, etc. So I understand the frustration. Do what is best for you. If this causes even more stress, then simply postpone your wedding. Remember, once you cross the border, you get another 6 months. So cross it tomorrow and you will be good for another 6 months, and can relax up to the day you get married.
I don’t want to get you muddled all up in the details, but it is information that helps and certainly would have helped me when I applied last year.
Best wishes.