Oh dear !!
I understand how you feel and your worries. I am married to a Canadian for almost 6 years now, but applying from abroad. I also have a daughter waiting in Canada for me to show up so I cannot risk a refusal. Well, I have been to Canada many times before on visitors visa, but never more than 2 months and never intended to stay in. I faced similar question at the border, but never been a problem as I could easily tell them I was there to visit my wife's family and I was always accompanied by my wife at the border and we both had return tickets.
If you are going to tell the officer at the border that you are going to see your boyfriend and accompany him for 6 months, I don't see how he will buy that false information. And as far as I understand false declaration will get you only trouble with Canadian government. I hope you will find a solution.
Also check this as PMM is a very competant person on immigration issues.
http://www.canadavisa.com/canada-immigration-discussion-board/waiting-for-permanent-residence-in-canada-t5484.0.htmlBest wishes and good luck with your marriage.