The US and Canada are replacing their military chiefs at about the same time. As each starts their term in office, observers can easily confuse what each can and cannot do. The striking difference is that the US Chairman can speak but not act and the Canadian Chief can act but cannot speak quite as much. Let me explain some of the differences and then some of the similarities.
The Canadian Chief of Defence Staff [CDS] is the commander of the Canadian Armed Forces. He is the ultimate authority, essentially, writing the rules of engagement, firing subordinates if need be, and providing the operational commanders with their missions.
The Chairman of the Joint Chiefs of Staff commands the Joint Staff ... and that is about it. His primary job is to serve as adviser to the President and the Secretary of Defense. He cannot order around the Combatant Commanders--the four star generals and admirals who command all of the US forces in their sector or function.
The CDS is appointed by the Prime Minister, and Parliament has no role in vetting him. Which means he is only accountable to the Prime Minister, but is answerable to Parliament. This answerability thing is actually quite limited since advice to cabinet is confidential. So, the CDS can speak about what the Canadian Armed Forces are doing and can do, but not what the CDS told the Prime Minister about what should be done.
The Chairman is appointed by the President but must be confirmed by the Senate. So, he is actually accountable to both the President and to Congress. This means that he can and occasionally must speak more broadly, depending on the questions asked by those in Congress.
How are they similar? Well, I used "he" a lot above since the American and Canadian military chiefs have been male. The time for a female CDS/Chairman is coming as more women are getting promoted to higher levels and with more women getting more experience commanding in combat, those numbers should increase even more. Still, not anytime soon.
How else? CDS's and Chairmen can range from being forward-leaning to acquiescent. The Chairmen, Myers and Pace, under Donald Rumsfeld experienced "mind melds", where they basically sold out to Rummy's stances on the issues. One could use many adjectives to describe the outgoing CDS but forward leaning is not one of them.
The two new leaders, US Marine General Joe Dunford and Canadian Army General Jon Vance, may or may not be that similar as chiefs (time will tell), but they do have some similar attributes. Both commanded in Afghanistan. Both are generally viewed as relatively blunt and assertive. Both have tough jobs ahead as they face more budgetary constraints in more complex times (the Cold War was more dangerous but far more simple). Both have to deal with messed up procurement processes (a widely shared dynamic among democracies these days). And both are starting their jobs during election season (although the US election is farther away, the campaign is very much underway). Dunford's boss will certainly change during his term in office, and might happen to Vance and maybe not.
Anyhow, as each takes over their respective militaries, we need to keep in mind that despite the common title of CHOD (chief of defense, in the NATO parlance), they have somewhat different jobs and definitely different expectations. The key commonality is that they will lead in interesting times.