We could fix this in the United States with just one Supreme Court holding that would be incredibly logical and reasonable. Currently, the entire logic of the financial surveillance state is that a person has no reasonable expectation of privacy in information that they voluntarily turn over to a third party such as a bank. Thus the government is entitled to that information without implicating the Fourth Amendment. Fair enough. But if I voluntarily turn over information to a third party pursuant to an enforceable agreement that the third party will use that information only as necessary for their internal business purposes and will otherwise endeavor to take all reasonable means to keep it confidential, then I absolutely do have a reasonable expectation that the third party will comply with the agreement and keep the information private. That's it. That's all it would take to demolish the modern financial surveillance state in the United States. It's reasonable, logical, not foreclosed by any precedent I know of, and (IMO) a contrary holding is not possible to reconcile with Fourth Amendment precedent. If you're interested in understanding how the Supreme Court looks at such cases, take a look at US v. Miller (no, not the 2A one), 425 U.S. 435 (1976).