Only once.
The chances of Canada being invaded by the US are non existent.
Invaded Mexico. See related questions.
Mexico
When the US invaded Mexico in 1914? Yes; those where the ABC countries (Argentina, Chile, Brazil) to prevent a new US-Mexico war.
The US, when it invaded the city and port of Veracruz.
The Zimmermann Telegram proposing an a german alliance with mexico if mexico invaded the US
Last time the US invaded Mexico by sea was during The Occupation of Veracruz, in 1914.
Five times: another way of looking at such size difference is that Mexico is roughly three times the size of Texas, or slightly larger than Alaska.
No, Mexico is about 1/4 the area of the USA
the California purhase was an offer to Mexico by the US to buy California around the early 1800's the Mexicans refused therefore the US invaded Mexico and gained California, Texas, Arizona, New Mexico, Colorado and etc
The US BORDERS Mexico.