You can have multiple SBC's connecting to the same tenant in different countries. Then users within 1 country can call out over their local SBC. This is all documented within the Direct Routing section at Microsoft.
One word of warning, you haven't mentioned which countries but you will need to check local jurisdiction rules as some countries your outbound call needs to leave within the country. E.g. User A in China wants to call User B in Italy so you might setup a dial plan that Italian calls go out over to the Italian SBC as this will result in a cheaper call. However, there may be a legal requirement that all calls have to go out of the SBC within its own country.