McG, your comparison list is a bit off. Most of my examples below will pertain to the infantry, but the general level of responsibility is there. As you can see, I advocate the current British System because it is the most simple and clear cut and it has some traditional value to our Army, which used it until unification.
If we wanted to do a direct comparison of rank and responsibility, it would look like this
Canada Britain United States
Private/Corporal Private All ranks of Private, Specialist/Corporal
Master Corporal Lance Corporal Sergeant
Sergeant Corporal Staff Sergeant
Warrant Officer Sergeant/Staff Sergeant Sergeant First Class
MWO Warrant Officer 2 Master Sergeant/First Sergeant
CWO Warrant Officer 1 Sergeant Major/Command Sergeant Major/
Command Sergeant Major of the Army
Here is a more detailed layout. The Royal Marines are exactly the same as the British Army while the United States Marine Corps is very similar to the US Army, with a few name changes (Gunnery Sergeant). Again, this pertains to the Infantry, but is mostly accurate for the other arms as well.
Canada has three levels of Privates: Pte (R), Pte (U), Pte (T). These all fall under the rank of Private. Obviously, Pte(R) is in training, Pte(U) is fresh to a unit, and Pte(T) is awarded his hook (in some units) as a competant soldier. All three are individual soldiers, with no additional responsibilities. All three of these levels fall under the single rank of Private, the nomials at the end are designators.
Britain has three classes of Private: Class 3, Class 2, and Class 1. These would be akin to our IPC codes, with some other qualifying characteristics (ie: in the Armour, a Trooper must have a certain amount of TI and get both his gunner and his driver course to be eligible.) All these Classes fall under the rank of Private as well.
The US has three seperate ranks of Private: Private (Pv1), Private (Pv2), and Private First Class (PFC). All three are separate ranks of private and are afforded separate paygrades; E1, E2, and E3 respectively. PV1 is for soldiers in Basic Training. I believe PV2 is given to graduates of Basic and PFC is akin to a Private Trained in Canada or Private Class Two in Britain, although I am not 100% sure.
Canada has the rank of Corporal, which is technically the first level of the NCO chain. However, as previously highlighted, there is no leadership requirement and TI is the real factor in promotion to Corporal. I understand it is done a bit differently in the Engineers, with Corporals actually needing a leadership course. Corporals, for the most part, are individual soldiers with no real responsibility. A glorified private in Canada
For the British, Lance Corporal is the first step into the NCO chain. I am unsure of whether it is an actual rank or an appointment. Either way, to become a Lance Corporal, one must pass leadership training and in the Infantry assumes duties as an Infantry section 2ic.
The British Corporal is the next step up in rank. A Corporal in the British Army undergoes further leadership training and is the true commander of field forces. In the Infantry, a Corporal is a section commander, commanding his soldiers within a Platoon with the help of his LCpl 2ic.
The Americans have a split at the paygrade of E4 between Corporal and Specialist. The way I understand it, specialist is akin to our Corporal, a glorified private, while an American Army Corporal is a soldier with basic leadership training that can assume a leadership role if required.
A uniquely Canadian position, the Master Corporal is an appointment, although it has become a de facto rank. Master Corporals in the Infantry are section 2ic's and must attend leadership training. The true bottom rung of the NCO.
In Canada the Sergeant is the first SNCO rank. In the Infantry, Sergeants are section commanders, who command with the aid of a 2ic (Mcpl).
In Britain, further leadership training can lead to promotion to Sergeant, which is the first SNCO rank in the British Army as well. A Sergeant acts as the top NCO in an Infantry Platoon/Tank Troop/Engineer Troop. He provides advice and correls the junior Lieutenants put in command of these units.
In America, the "buck" Sergeant is the first level of command. An American Sergeant (E5) usually commands an infantry fire team, which 2 or 3 usually make up a squad.
Canada abandoned the rank of Staff Sergeant upon unification. Warrant Officers will fill out the roles that were covered by this rank.
In Britain, a Staff Sergeant, or a Colour Sergeant in the Infantry, is a staff level NCO. They often perform the roles as Platoon Sergeants, but can also serve as NCO's in unit staffs as well as taking on the key position of CQMS, running company stores and weapons.
In the United States, a Staff Sergeant (E6) is the Squad Leader, commanding a unit composed of fireteams, which he directs through his Sergeants. A Staff Sergeant fulfills the duties of a Canadian Sergeant and a British Corporal.
From here on, the ranks take a big diversion among the three militaries, I'll try and sum it up as neatly as possible.
Platoon NCO (Canada and US)
The Canadian Warrant Officer (WO) fulfills the role of Platoon Warrant. Fulfilled by a Sergeant in the British Army, a Warrant will act as top NCO in a platoon as well as filling out the duties accomplished by a British Staff Sergeant (Staff duties, CQMS)
The American Sergeant First Class (E7) is very similar to the Canadian Warrant Officer, filling out similar duties as Platoon Sergeant.
In Canada, the Master Warrant Officer acts as the Company Sergeant Major, head NCO in the company responsible for the skills, discipline, and dress and deportment of the other ranks in the company.
In Britain, the rank of Warrant Officer 2 (WO2) does the same thing as a MWO, acting as CSM.
In the US, the rank grade of E8 is split between Master Sergeant and First Sergeant. Both are the same rank level, but have different responsibilities of command, of which I am unsure of how it works. I do know that First Sergeants are the Company NCO's, often refered to as "Top Kicks" or "First Shirts", they do the same thing as a Canadian MWO in the CSM role.
Higher Level NCO's
In Canada, the Chief Warrant Officer is the highest rank for an NCM. A CWO can be appointed as a Regimental Sergeant Major, the top NCO in a battalion level formation (called Regiment in the other arms). As well, CWOs can act as Sergeants Major in larger formations (Brigade), bases, and the right hand man of the Chief of Defence Staff, the Canadian Forces CWO (top NCM in the CF).
Britain has the same roles performed by a Warrant Officer 1 (WO1).
In the US, the highest enlisted pay grade of E9 is divided into three ranks: Sergeant Major, Command Sergeant Major, and Command Sergeant Major of the Army. I believe Sergeants Major act at battalion level (Canadian RSM), Command Sergeants Major act at Brigade and Division Levels (our formation and base CWO), while the Command Sergeant Major of the Army is the highest enlisted rank in the Army.