For massive daily data transfers (250 TB) between cloud providers, traditional VPNs or routing through on-premises "hairpinning" are inefficient and costly. Cross-Cloud Interconnect is the architecturally correct solution for high-bandwidth, low-latency, and secure cloud-to-cloud connectivity.

According to Google Cloud Documentation (Cross-Cloud Interconnect Overview):

"Cross-Cloud Interconnect helps you establish high-bandwidth dedicated connectivity between Google Cloud and another cloud service provider (CSP) such as Microsoft Azure... It simplifies multi-cloud setup by providing a direct physical connection between Google's network and the other CSP's network."

Calculation of Requirement:

Data Volume: 250 TB per day.

Time: 86,400 seconds (1 day).

Required Bandwidth: $250 \times 10^{12} \text{ bytes} \times 8 \text{ bits/byte} / 86,400 \text{ seconds} \approx 23.1 \text{ Gbps}$.

A standard VPN (Option B) typically caps out at 3 Gbps per tunnel, making it insufficient.

The existing 20Gbps Interconnect (Option C) is already used for on-premises data and would be overwhelmed by an additional 23.1 Gbps requirement, not to mention the latency of routing Azure traffic through an on-premises data center.

Why other options are incorrect:

B is incorrect: VPN throughput is insufficient for 250 TB/day and lacks the reliability of a dedicated circuit.

C is incorrect: Routing through on-premises (hairpinning) introduces unnecessary latency and would exceed the 20Gbps capacity of the existing Interconnect.

D is incorrect: SFTP over the public internet is neither efficient for petabyte-scale data nor as secure as a private interconnect.