Am I allowed to sublet my unit in a non-profit housing co-op in Ontario?

Generally not without the co-op's approval, and often not at all. Non-profit housing co-ops are built around the idea that members actually live in their units rather than acting as landlords to someone else, so most co-ops' bylaws and occupancy agreements either prohibit subletting outright or allow it only in narrow, board-approved circumstances, such as a temporary absence for work, school, or medical reasons.

This is different from a typical rental tenancy, where a tenant generally has more flexibility to sublet with a landlord's consent that can't be unreasonably withheld. Because a co-op's whole funding and community model can depend on units being occupied by actual members rather than sub-tenants, moving out and subletting without going through the co-op's approval process can put your membership itself at risk, potentially leading to termination proceedings under the co-op's bylaws. If you're considering a temporary absence and want to keep your unit, the right approach is to raise it with the co-op's board well in advance and follow whatever approval process the bylaws set out, rather than arranging a sublet informally and hoping it goes unnoticed.