Wow, they wont accept it if you mention you plan to marry. Don't think we did. But I'll look over everything again, just to be sure. We're not getting married for the paperwork. So we're not going to go off and do that, and change it to spousal sponsorship.
How long have you been in this relationship? Is the relationship common knowledge to all your friends and family members? Have you lives become intertwined on all levels including financial, i.e. join bank accounts, insurance policies, wills, etc.?
If I recall correctly, Allison's application was solid because of significant proof of all of the above. Have you read OP Manual 2? You might want to give that a look.
http://www.cic.gc.ca/english/resources/manuals/op/op02-eng.pdf