Section 54 of the
Forest and Range Practices Act:
"A person must obtain the consent of the minister before
constructing or occupying a buiding or other structure
on Crown Land in a Provincial Forest unless the construction
or occupation is authorized under another enactment."
Section 57, Forest and Range Practices Act:
...a person must not (construct, rehabilitate or maintain)
a trail or recreation facility on Crown Land.
So don't feel awkward around an illegal cabin. The builder
has no exclusive right to use the cabin and you should
not feel that the builder has any right to keep you away.