I don't really know why people keep saying Canada or Mexico. Canada is bigger? We have 10X the population. And our population is about 3X that of Mexico, so even if they joined up we'd still have twice the amount of manpower, so flanking doesn't matter much.
More statistics: 45% of American households are believed to have guns, which comes out to about 206 million total guns.
On the other hand, roughly 26% of Canadian houses have guns, which comes out to about 15 million guns.
Can't find a statistic on how many guns are in Mexico, mostly because all the related statistics are about how many guns Mexico gets from the US. Some statistics say 36%, others say 90%. Either way it's a lot.
This isn't even taking into account the military.
America: Army 507,158
Navy 347,693
Air Force 347,352
Marines 179,762
Coast Guard 41,002
Reserves 1,000,000
Paramilitary 53,000
Total for US Military 2,475,967
Now how about Canada?
Active personnel: 66,949 (ranked 58th)
Reserves: 19,290
Total: 86,239
And Mexico?
Currently, Mexico's armed forces number some 620,400, including the reserves.
I'll even round up to do a bit of math here.
Canada's 100,000 + Mexico's 750,000 = 850,000.
[That's a lot of rounding up]
...I'll round down to compare... That's still nowhere near the 2,000,000 in America's military.
Here's a list of countries currently possesing WMDs, or nukes of you will. United States, Russia, United Kingdom, France, China, India, Israel, Pakistan, North Korea. See Mexico OR Canada on that list? No!
So, please, enlighten me onto exactly how Canada or Mexico, even if they joined
forces, could possibly stand any kind of chance against the US.