Cultural imperialism is "we'll all do things my country's way because it's the best way to do it".
"I like playing your country's music, and you like playing my country's music, and ain't it cool that we both like this stuff" is not cultural imperialism...
So to use a loose analogy, McDonalds is cultural imperialism, whereas Coca-Cola isn't. Mickey D's dictates that all their fast-food restaurants shall look like this, and all the staff shall dress like this, and this kind of food shall be what we serve. If a McDonalds looks out of place in a historic European city - screw it, build it anyway. But sugary drinks aren't inherently tied to a culture (unlike food), and Coca-Cola don't dictate what the places that it's served look like, or how it's served, so it's an addition to the locally available tastes rather than being intended as a replacement.