Technically you should file your tax return to QC government if you held a QC residential address on Dec 31, 04.
Your landlord has to claim rental income but you don't have to claim rent, since the government doesn't care if you claimed tax credit on rent. it's actually in their favor if you don't claim.
you can have a different address from your husband's which is called "involuntary seperation". this refers to spouses who have to live seperately even they didn't break up. check the CRA pamphlet and you'll find pertinent explanations.
if you moved in with your relative during 2004, you can declare you address change in your tax return and file an Ontario return.
if your employer requires you to be an Ontario resident in order for them to claim certain provincial tax credits, then they may ask you to sign a declaration form regarding your principal address, and remember misrepresentation is against the law.