This technical paper examines the supplier evidence gap faced by Brazilian companies exposed to European value chains under the EU-Mercosur trade architecture, CSDDD/CS3D, CBAM, EUDR, CSRD/ESRS and related buyer-readiness pressures. The central thesis is that market access does not automatically create supplier eligibility. Brazilian suppliers may become more commercially visible under EU-Mercosur trade expansion while remaining vulnerable to exclusion, delay, price pressure or contractual friction if they cannot provide audit-grade, buyer-readable evidence on origin, traceability, emissions, deforestation risk, due diligence, waste, reverse logistics, ITAD and governance controls. The paper introduces the EU-Brazil Supplier Evidence Defensibility Framework, a structured approach for converting Brazilian operational execution into European regulatory defensibility. It is designed for CFOs, boards, procurement teams, compliance functions, exporters, industrial suppliers and companies exposed to EU-facing supply chains. The analysis is technical and strategic. It does not constitute legal, tax, customs, financial, investment or audit advice. It does not promise legal compliance, buyer approval, avoidance of sanctions or risk elimination. Its purpose is to support regulatory risk interpretation, evidence architecture, supplier-readiness analysis and board-level decision-making.