Why is it called "Canada/US border and US /Mexico Boundary? what's the difference?

The answer is very simple and not at all sinister -

Canada/US border is the geopolitical boundary between the nation of Canada and the nation of the United States.

US/Mexico border is the geopolitical boundary between the nation of Mexico and the nation of the United States.

"...Are the governments getting ready for a North American Union?..."

There already is one. It's called The Organization of American States (OAS)

Border protection is a humorous tale era. however the main important problem is presently at our southern border. With mexico's depressed financial equipment sneaking into the U. S. is somewhat eye-catching. Canadians on the otherhand, dont have the tousled government and economic equipment that the mexicans do and consequently have little impetus to illegally enter the U. S.. This actuality does not whether do away with the would desire to safeguard ALL of our borders. the opportunity of terrorists shifting risky components over the two border is unacceptable, and the unlawful get admission to of distant places nationals would desire to be stopped in spite of national beginning.

The difference is pretty obvious.

There is no North American Union being planned.

I've heard it called both way. Remember the song "Down by the border, by Mexico way?"

As for a Union, the black heliocoptors are down for repair.

1) There is no difference.

2) Yes.