Section 46 of the Criminal Code has two degrees of treason, called "high treason" and "treason."
It is pretty clear that anyone who assists forces in active combat with Canadian Forces is liable for High Treason. No amendment of the Criminal Code is necessary -- what is needed is the political will to prosecute.
Section 46 of the Criminal Code reads as follows:
(1) Every one commits high treason who, in Canada,
(a) kills or attempts to kill Her Majesty, or does her any bodily harm tending to death or destruction, maims or wounds her, or imprisons or restrains her;
(b) levies war against Canada or does any act preparatory thereto; or
(c) assists an enemy at war with Canada, or any armed forces against whom Canadian Forces are engaged in hostilities, whether or not a state of war exists between Canada and the country whose forces they are.
(2) Every one commits treason who, in Canada,
(a) uses force or violence for the purpose of overthrowing the government of Canada or a province;
(b) without lawful authority, communicates or makes available to an agent of a state other than Canada, military or scientific information or any sketch, plan, model, article, note or document of a military or scientific character that he knows or ought to know may be used by that state for a purpose prejudicial to the safety or defence of Canada;
(c) conspires with any person to commit high treason or to do anything mentioned in paragraph (a);
(d) forms an intention to do anything that is high treason or that is mentioned in paragraph (a) and manifests that intention by an overt act; or
(e) conspires with any person to do anything mentioned in paragraph (b) or forms an intention to do anything mentioned in paragraph (b) and manifests that intention by an overt act."
It is also illegal for a Canadian citizen to do any of the above outside Canada.
The penalty for high treason is life imprisonment. The penalty for treason is imprisonment up to a maximum of life, or up to 14 years for conduct under subsection (2)(b) or (e) in peacetime.
Proposals to strip those convicted of Treason of Canadian citizenship are problematic. Ignoring constitutional concerns (which can probably be addressed) removing citizenship could lead to the weird result that subsequent acts against Canadian Forces (by former citizens) are lawful.
The better response?
Prosecute for treason in those very very rare cases where appropriate:
Stephen Harper's governing Conservative Party will debate whether Canadians should be stripped of their citizenship should they take up arms against this country or its allies.
It's one of a multitude of proposed changes to the Conservative Party's official policies up for debate when Tories from across Canada converge in Ottawa for a June 9-11 convention.