Can my Ontario commercial landlord refuse to consent to an assignment without a good reason?

It depends on exactly how your lease's assignment clause is worded, which is really the crux of this question. If the lease requires the landlord's consent to an assignment but is silent on the standard for refusing it, courts have generally been prepared to read in a requirement that consent not be unreasonably withheld, giving the tenant a real basis to challenge a refusal that isn't tied to a legitimate concern, such as the proposed assignee's financial capacity or suitability for the space.

However, a well-drafted commercial lease can validly give the landlord much broader discretion, including the right to withhold consent in its sole or absolute discretion, in which case the tenant has far less ability to challenge a refusal, even one that seems unfair. Courts generally respect that kind of clear contractual language rather than overriding it with a general reasonableness requirement.

Before assuming a refusal is improper, or trying to push forward with an assignment despite a landlord's objection, read the specific wording of your lease's assignment clause closely. Whether "reasonable" or "absolute discretion" language governs makes a real difference to how strong your position actually is.