Please correct me if I'm mistaken. I am under the impression that you cannot apply for Express Entry if you are:
"a grand-parent, parent, spouse, or common-law partner of a Canadian citizen or permanent resident living in Canada, an applicant under humanitarian and compassionate grounds, a refugee claimant or a failed refugee claimant;" NOVA SCOTIA DEMAND: EXPRESS ENTRY STREAM
My husband and I looked into this possibility as well, however, as you move forward in the Express Entry application process, it begins to ask questions about whether or not you are married, and it assumes you will be traveling with your spouse. It did not give any ability to say your spouse is Canadian. Why? We figured because it is assumed you will apply under Spouse Sponsorship rather than FSW.