Does my Ontario commercial lease need the landlord's consent before I can sublet?

Almost certainly, yes, though the answer ultimately comes from your specific lease rather than a general rule. The great majority of Ontario commercial leases include a clause requiring the tenant to obtain the landlord's written consent before subletting all or part of the leased space, and courts generally won't imply an unrestricted right to sublet against wording that clearly requires consent.

Where the lease requires consent but doesn't say the landlord can withhold it for any reason, courts have generally been willing to read in a requirement that consent not be unreasonably withheld, giving a tenant some recourse against an arbitrary refusal. But a carefully drafted lease can validly give the landlord broader, even absolute, discretion over subletting, in which case the tenant has much less room to push back on a refusal.

Because the actual wording of your lease's subletting clause determines both whether consent is needed and how much room you have to challenge a refusal, review that specific language, rather than a general expectation about what's "normal," before assuming you're free to sublet or that a landlord's refusal must be reasonable.