Dedicate extensions to outbound routes / trunks

I did not find enough information specific to my question. Could I get some clarification that is not over a year old? Thank so much!

How do I dedicate extension 100 to outbound route/trunk A and extension 2001 dedicated to outbound route/trunk B?

If I do not use extensions and just DIDs, can I setup the extensions “user extension” using the actual DID?

Thanks again.