Theravada is dispersed over a very wide area covering cultures in Cambodia, Sri Lanka, Burma and Thailand to name a few. The situation is even more complicated in Mahayana where it is practiced in countries as culturally distinct as Tibet, China and Japan. Meanwhile, internal to each of those countries you have a range of different ethnic groups, different historical religious and ritual practices each of which has its own influence on Buddhism. For example, in Tibet you have the Bon religion which was the main religion prior to the introduction of Buddhism. That has heavily influenced some of the Buddhist tenet schools there. In Sri Lanka, you have Theravada, yes, but the Hindu practices of the sizeable Tamil population has significant bearing on how Buddhism is also practiced.
So I just think the question is rather hard to answer because (a) it supposes that Theravada and Mahayana Buddhism are each very distinct traditions that are practiced the same way in different countries, and (b) it supposes that there is some cultural continuity internal to Mahayana countries and also Theravada countries. But the fact is that the composition of each of those countries is extremely diverse making it virtually impossible to make any general statement about those different nations. It would be like asking “what is the cultural similarities between all Christian nations globally?” And the answer would be something pretty generic such as “They all believe in the authority of Christ, the authenticity of revelation and each of those countries has been influenced by its Christian heritage.” Beyond that any more fine grade analysis would require a detailed discussion of the individual country. The only thing that is really in common, say, between Mahayana countries theoretically - and I say that because it is not clear actual practitioners would necessarily pay any heed to this - is that all forms of Mahayana Buddhism accept the bodhisattva ideal and they accept the authenticity of esoteric sutra documents. That is probably the main theoretical difference. Likewise, forms of Theravada Buddhism all agree in theory that their Buddhism is based upon the Pali canon and is therefore, in their eyes, “original Buddhism”. (Even though that’s not really true).