http://www.cra-arc.gc.ca/E/pub/tg/t4...DME.html?=slnk
Read up on this first. If you declare rental income, yes, you can write off a percentage of the house expenses against that income.
But then, you lose part of the principal residence exemption when you come to sell the house. For example, 1/5th of the house might be considered rental, so 1/5th of the capital gain/loss would have to be reported. It would be up to you to keep track of what you paid for the house and land, how many years would be considered rental, and how much would be considered capital gain/loss when you sold.
Any net profit would be added into your income and taxed at whatever rate you fall into.
If you are renting to a friend who will help out with the expenses, then this is not necessarily considered rental income, as you would not intend to make a profit on the situation. No income would be claimed by you or credits claimed by him. I don't know if Manitoba has a rental/property tax credit like Ontario does, so I am speaking from an Ontario point of view.
If you have a lease agreement, this leans more towards a rental agreement, so make sure you charge enough in the first place. Add up your expenses, prorate them, and charge enough to at least cover these. Make sure you have a very clear agreement about the groceries. Who buys, who cooks, who cleans up, do you put names on stuff in the refrigerator?
If you are friends, this could get complicated. Make sure both of you have an exit strategy in case the friendship goes south.