Only if you have a stated, defensible reason — unless your own lease says otherwise.
Short answer
Usually only for cause. Ontario's Commercial Tenancies Act implies that a landlord cannot unreasonably withhold consent to a lease assignment, unless the lease itself hands the landlord sole or absolute discretion. Which one applies to you is a question about your specific lease clause, not a general rule.
The baseline, per treadstonelaw: “under the Commercial Tenancies Act, a landlord cannot unreasonably withhold consent to an assignment, unless the lease explicitly takes away that right or the proposed assignee is genuinely unsuitable.” But that default is easily displaced: “unlike the residential context, commercial lease terms can specifically override or expand the statutory baseline — so your lease controls.” Where the lease grants the landlord sole or absolute discretion over consent, “the implied 'not unreasonably withheld' standard generally doesn't apply, and the landlord may have much broader latitude to refuse.” Read your own consent clause before assuming either rule governs.
Before consenting, a landlord can typically require financial evidence that the buyer can meet the rent, a personal guarantee from the buyer's principals where the buyer is thinly capitalized, a new or increased security deposit, confirmation the buyer's intended use still fits the lease's permitted-use clause, an estoppel certificate from the seller confirming the lease is in good standing, and coverage of the landlord's own legal costs for reviewing the consent. Some landlords also use the request as leverage to renegotiate the term or rent as “the price of consent.” What counts as unreasonable is fact-specific: “a landlord who refuses without stated grounds and without exercising a recapture right may be acting unreasonably.”
A tenant sells its restaurant business and wants to assign the lease to the buyer. The landlord reviews the buyer's financials, sees thin capitalization, and asks for (a) a personal guarantee from the buyer's principal and (b) confirmation the buyer will not convert the space to a concept outside the permitted-use clause. That is a defensible refusal-to-consent-until-satisfied. If the landlord instead simply says no, states no reason, and does not exercise a recapture right, that likely crosses into unreasonable refusal — assuming the lease preserves the statutory standard in the first place.
The mistake runs in both directions: tenants assume the “not unreasonably withheld” standard always applies, and landlords sometimes forget it might not. If the lease grants sole discretion, the statutory default is displaced and the landlord's latitude is much wider. This is Ontario's Commercial Tenancies Act framework specifically; other provinces set their own assignment-consent standards by statute and common law.
Related: distraining for unpaid rent and a missed renewal deadline are two other lease-continuity questions worth reading alongside this one.
Whether your lease preserves the reasonableness standard or displaces it changes what you can ask for.
