This has been tossed about a lot in the past, and in the '60s, was almost considered a slam dunk.
However, curiously enough for such two similar regions, a number of things have changed since then.
America has moved relentlessly to the political right, to the extent that things like universal medical care, for example, (even Nixon went for that), once considered, is now looked on as little better than communism. There are two political parties currently in the US: one a little to the right of the political center, and one a little to the right of Attila the Hun. All other voices in what should otherwise be a cacophony of divergent opinion, in a nation of 315 million, are submerged, beaten down, ridiculed, paid off, or otherwise seen by common wisdom as being ridiculous.
In Canada, there are five major federal political parties, three of which could possibly form government. They represent a relatively broad philosophical spectrum.
Today Americans are arming themselves to the teeth, with debates about allowing guns into churches, schools, universities, hospitals, etc; whether one should hide their gun in a pocket or purse; whether it is ok to carry an assault rifle into the supermarket, or to a political rally. Not surprisingly, gun deaths are in close coordination with guns in circulation.
In Canada, the wild west lives on in movies, but not in the streets. Guns are regulated, and hand guns are almost unknown aside from a few very select occupations, and a small handful of sportsmen, the latter under regulations that would have the NRA recreating the storming of the Bastille, this time with the White House as the target. Needless to say, gun deaths are proportionately lower.
The answer to crime in the US is imprisonment, and the US has the highest rate of incarceration in the world. People are locked up for long periods, sometimes on the most dubious indications. At any one time, close to one percent of the US population can be under lock and key.
Prevention and counselling take a stronger role in Canada, and incarceration rates are far less. Imprisonment is seen as a last resort.
In the 1960s, ideas about religion were about the same in both countries. We have strongly diverged since then. Most Americans today profess some sort of metaphysical belief, and many are deeply immersed in religious dogma.
In Canada, about a third of the population professes no religion, and among the rest, belief can be soft to the point of non-existence. It is usually only a small minority of recent immigrants that actually practice such beliefs.
So should they be one country? Maybe, but some movement on the American side would be necessary before such a measure is taken, IMO.