Section 2 of the Builders Lien Act defines what the lien is against, and it is not just the land:
Subject to this Act, a contractor, subcontractor or worker who, in relation to an improvement,
(a) performs or provides work,
(b) supplies material, or
(c) does any combination of those things referred to in paragraphs (a) and (b)
has a lien for the price of the work and material, to the extent that the price remains unpaid, on all of the following:
(d) the interest of the owner in the improvement;
(e) the improvement itself;
(f) the land in, on or under which the improvement is located;
(g) the material delivered to or placed on the land.
(Builders Lien Act, s. 2(1)).