Harris has scored four goals in four Sky Bet Championship games, earning a Wales call-up for the first time sine the 2022 World Cup in Qatar, when he failed to make an appearance.
The 25-year-old striker, who has five caps, last represented his country in June 2022.
Wales host Turkey in a UEFA Nations League clash tonight, before visiting Montenegro in the same competition on Monday evening.
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U’s head coach Buckingham said of Harris: “He deservedly goes into a Wales camp, and can go and enjoy himself, and show what he’s about there.
“I’m delighted with him. Anyone that comes to the games can see how important he is to everything else that we do as well, whether it’s on the ball, but certainly his smartness and work rate without the ball.
“That’s so important to us as a group. He sets that tone from the front.
“He’s a good finisher. The most important thing since I’ve come into the club is trying to keep him in those goalscoring areas.
“That’s something he’s worked extremely hard on, and if we can keep him in between the posts, or in between the six-yard box as much as possible, that’s what he’s capable of doing.
“There will be times when I ask him to do other things, like against Norwich when he ran different channels, but the more we can keep him in the box, the better.”
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Buckingham added: “I’ve worked with different forwards in different teams, and when I came in, he was a player that we felt could really complement what we do as a team.
“We know he can finish, but what I saw when I came in was him spending a lot of time outside the box.
“We changed the formation and way we set up to try and allow him to stay central, and allow others to create for him, because we know if we can get him in the box, the range of finishing he does have.
“In terms of with the ball, he allows us to build, and he’s getting better at that build-up play and coming to link, and involve those around him, to allow us to get up the field in a different way.
“We know out of possession is going to be so important this year to us, against very good teams.
“His work rate is second to none, but it’s his smartness with how he works. He really allows us to do what we do.”