Context: Patients with access to a primary healthcare (PHC) provider benefit from better care and health outcomes. However, 15% of Canadians, classified as “unattached”, do not have a regular PHC provider. Seven Canadian provinces use Centralized Waitlists (CWLs) to coordinate linking unattached patients (UPs) to a PHC provider. CWLs remain under-evaluated, and it is unknown how well CWLs attach patients to PHC providers and which component attributes and processes facilitate CWL success. Objective: Determine the effectiveness of CWLs in Nova Scotia, Ontario and Québec in attaching patients to regular PHC providers. Mixed-Methods Study Design: Data collection includes linkage and analysis of CWL and administrative health data; policy reviews; qualitative interviews with knowledge users, patients and providers; and facilitation of stakeholder dialogues to identify CWL causal pathways, determine their effectiveness and elicit recommendations for improving CWL attachment. Setting: Administrative data and community-based qualitative data with integrated knowledge translation across the three Canadian provinces. Population: All UPs registered on the three provincial CWLs are included in the quantitative phase. Totals of 10 knowledge users; 10 patients registered or who have been registered on the CWLs; 10 PHC providers accepting patients from the CWLs; and 20 other key stakeholders per province are included in the qualitative phase. Outcome Measures: Quantitative: Primary outcomes include patient attachment rate and time to patient attachment; provider participation rates with CWL. Secondary outcomes include observed changes in patients’ emergency department and PHC visits pre/post attachment. Policy Scan: relevant policies impacting PHC access across three provinces. Qualitative: perceptions and experiences with patient attachment to PHC across patient, provider and policy maker perspectives. Results: This research will capture and delineate contextual and modifying factors influencing patient attachment, revealing components, processes and environments promoting PHC attachment via CWLs between and within provinces. These findings will determine the impact of attachment via CWLs on healthcare utilization. Finally, this research will generate patient, provider and policymaker-informed recommendations. Outcomes to be Reported: What, how and why variations in attachment outcomes exist across three provincial CWLs; implications for policy and practice within PHC.