Can a subcontractor lien a property even if they never contracted directly with the owner in Ontario?

Yes. Construction lien rights under the Construction Act don't depend on having a direct contract with the property owner - a subcontractor who contracted only with the general contractor, or a supplier who contracted only with a subcontractor, can still register a lien directly against the owner's property for unpaid work or materials that improved it. The lien attaches to the property itself because of the improvement made to it, not because of any direct contractual relationship between the lienholder and the specific party who owns the land.

This is one of the features that makes construction liens unusually powerful compared to an ordinary breach of contract claim, since an owner can end up facing a lien from a subcontractor or supplier they've never dealt with directly and may not even know exists, which is part of why the statutory holdback system exists - it gives owners and general contractors a built-in reserve to help satisfy exactly these kinds of claims from parties further down the chain. The same strict preservation and perfection deadlines still apply regardless of the lack of direct contractual privity, so a subcontractor or supplier in this position needs to track the relevant trigger dates just as carefully as anyone else in the contracting chain.