How do two co-owners of a rental property each report their share of the rental income?

Each co-owner reports their proportionate share of the rental income and expenses based on their actual ownership interest in the property. If you own the property 50/50, you'd each generally report half of the income and half of the deductible expenses on your own tax return; if the ownership split is different, the reporting should reflect that actual interest, not an even split just because there are two owners.

The key word is "actual" - your reported share needs to reflect real ownership and economic interest in the property, which usually traces back to how the purchase was funded and what's reflected in the ownership documents, rather than being something the co-owners simply agree to allocate however is most convenient at tax time. Each owner also handles their own CCA claims and other elections separately, since you're each filing your own return with your own share of the numbers. Keeping clear records of the ownership percentage, how the purchase was financed, and how income and expenses are actually split day to day makes this straightforward to support if CRA ever asks about it.