I was multitasking when I heard this on TV and am not sure whose ad it was - I'm thinking perhaps Wendy's - but thought the terminology was intriguing. Perhaps this is in reaction to U.S. consumers' fears about imported foods, courtesy of the problems with China-sourced food contamination, and/or to the NY Times article about the risk of E. coli in ground beef and the multiplicity of sources that may be represented in a single package of meat. "North" could do with a little parsing. I suspect that in this case it is hoped that consumers will think that is synonymous with the U.S. and perhaps Canada, which many Americans don't regard as a foreign country, and equate with "safe". But for these purposes it likely includes Mexico and perhaps Central America (countries north Colombia). There's a lot of anti-immigrant sentiment in the U.S. - often boiling down to anti-Mexican/Latino.
Maybe I'm being too cynical, but the terminology struck me as xenophobic. Considering our expectation of year-round fresh produce availabilty, and the international sourcing of ingredients in processed foods, it is ridiculous to imply that "North American" is inherently superior to foreign-sourced. I believe that by including that phrase in the burger ad, the company was trying to make that distinction.