I don't know by direct, in house experience. I do know that friends have 2 sons from Russia and they are great kids, but they have had to overcome their early years in orphanages (one was under 2 and one was under 4). They have worked with local professionals to overcome ADHD-like behavior and language problems.
My cousin was an infant adoption from South Korea. My aunt and uncle tried to adopt domestically for years before going overseas and they did so because a failed placement was too hard on their other kids. The last one the grandmother convinced the mother to take the kid back during the wait period. After that my aunt and uncle decided to only go for adoptions where the parental rights were terminated and my cousin was in an orphanage.
I have other friends who would like to adopt kids in the foster care program, but have not been matched. They would like siblings, but their son is 7 and the adoption program doesn't want to upset the natural order, so they don't want to place a sibling set where the biological son would be the youngest or middle child. So they are waiting.
You also need to talk to agencies about things like open and semi open adoptions. My friend's son is in a semi open adoption. She knows his family. She gets annual updates from his grandmother, but she does not visit, call or write. He can find her when he's 18 if he wants to. You have to be honest about your level of openness and not lie to say you can do x and really never have the visits the birth parents hoped for. Personally, I struggle enough as a stepparent so I would not want an open adoption. I would want a kid to be able to have information later, but the relationship in the younger years would not be something I could do. Some birth parents want a very closed adoption (no info later, please don't contact, etc.) and so it can go both ways.
Adoption can be an expensive and lengthy process (my aunt said the 2 years was the longest gestation ever). I personally think it is better when it is not a secret. My cousin knows he was chosen and has no shame in being adopted.
So...bottom line...start checking out agencies, going to meetings and talking with other parents who have used those agencies to gauge their experiences. Make sure this is a step you as parents want to do and it's not really about your son wanting a sibling (and perhaps he won't get the exact kind of sibling he dreams of, either...) Perhaps it is a quibble but you said "love like our own". I would keep talking til you can definitively say "as our own". I was adopted by my stepfather and when my sister came along, I felt the difference between like and as, not just from him but from the extended family. You should also think about how your families will react and if they are reticent, how you will handle that and keep the child from feeling less-than.
I overall think adoption is a good thing, and wish you all the best in your journey.