Hello!
Just because a company, like Mcdonald's, has it's origins in the US, does not mean a US citizen is guaranteed a job there. Remember that you are in another country. You must be a citizen, usually, to get these kinds of jobs. How do I know? Because I have tried, or have asked about it. I'd go for an international company, and try to contact the US embassy to ask if they know any, or can help you get hired. Of course, the best way is to start paperwork, or get hired, from your home country, the US, before you arrive.
Another option is to look for bilingual jobs, but you must speak at least intermediate Spanish for these jobs. Or, a last option could be a job as a English conversational teacher, if you are not a certified citizen teacher, you will not be hired by official institutes. So go for private institutes.
Hope I could be of some help!