Tony mentions that the body in Arlington isn't really Cap's, but a decoy to please the public, and that this funeral would have been what Steve really wanted. The real body is here, and it will rest in the Arctic forever, the rationale being that he was preserved in peace here for decades until he could be revived, and so it was the best place for him to rest forever.
Tony mentions that the Arlington body isn't Cap's actual remains but a decoy to satisfy the public. This funeral would reflect what Steve truly wanted. The real body is here and will rest in the Arctic forever; the rationale being preservation for years until revival, making this his ideal resting place.