Subsection 494(2) adopts or cross-references with section 25 of the Criminal Code, so it's the same standard of force. I'll just go back to section 25 to get the proper wording. Section 25 refers to somebody who is doing:
anything in the administration or enforcement of the law
(a) as a private person,
(b) as a peace officer or public officer,
(c) in aid of a peace officer or public officer, or
(d) by virtue of his office,
is, if he acts on reasonable grounds, justified in doing what he is required or authorized to do and in using as much force as is necessary for that purpose.