If I rent and sublease to make my rental payment is this income?

It's a bit of a trick question. CRA's web site has no clear direction on this. I think because they don't want to leave any loopholes for people to crawl through. Instead they simply seem to treat everything as rental income.

But in practice I think the kind of situations you describe generally go unreported, and CRA doesn't do anything about it, because there is no Net Taxable Income. For example, suppose you reported your roommate's contribution to the rent as rental income. But you would be allowed to deduct as an expense a proportionate share of the rent you are payng the landlord as your "cost" of providing your roommate's space. So you have no net rental income. I believe the 1-2 week sublet would fall into the same category.

Your ex's lawyer is not asking just about taxable income though. He is trying to get data on your actual living costs and income as it affects your ability to pay support. For example you can't claim you need $2000/month to pay for your condo if in fact you have a roommate who is paying half.

In any case you should be talking to your own lawyer, not us amateurs, particularly if your financial circumstances have significantly changed from your original settlement.

Your situation with a roommate is more like a joint tenancy agreement than a typical rental situation. According to the Landlord & Tenant board tenancies can be verbal and just as legal.

I don't believe that CRA would consider that you are a "landlord" in the business of renting out apartments. First of all every business requires the expectation that some profit would be realized. You would also be allowed to claim some office expenses, mileage, perhaps decorating expenses and other items of such a nature. Secondly there is a requirement that businesses be legal and such a business would not be. In Ontario you are not allowed to "sublet" your apartment for more than you pay. So for instance if you find a waterfront condo for $600 per month you are not allowed to rent it for $1200 to someone else. You are also not allowed to rent a house with 4 rooms for $1500 and then rent each room for $500. People do it but it is not legal. This is legislation left over from when rent control was in effect and people were doing that.

I know this is clear as mud but I hope it helps