In 2016, two Canadian hospitals participated in a quality improvement (QI) program, the International Acute Care for Elders (ACE) Collaborative, and sought to adapt and implement a transition coach intervention (TCI). Both hospitals were challenged to provide optimal continuity of care for an increasing number of older adults. The two hospitals received initial funding, coaching, educational materials, and tools to adapt the TCI to their local contexts, but the QI project teams achieved different results. We aimed to compare the implementation of the ACE TCI in these two Canadian hospitals to identify the factors influencing the adaptation of the intervention to the local contexts and to understand their different results. We conducted a retrospective multiple case study, including documentary analysis, 21 semi-structured individual interviews, and two focus groups. We performed thematic analysis using a hybrid inductive-deductive approach. Both hospitals met initial organizational goals to varying degrees. Our qualitative analysis highlighted certain factors that were critical to the effective implementation and achievement of the QI project goals: the magnitude of changes and adaptations to the initial intervention; the organizational approaches to the QI project implementation, management, and monitoring; the organizational context; the change management strategies; the ongoing health system reform and organizational restructuring. Our study also identified other key factors for successful care transition QI projects: minimal adaptation to the original evidence-based intervention; use of a collaborative, bottom-up approach; use of a theoretical model to support sustainability; support from clinical and organizational leadership; a strong organizational culture for QI; access to timely quality measures; financial support; use of a knowledge management platform; and involvement of an integrated research team and expert guidance. Many of the lessons learned and strategies identified from our analysis will help clinicians, managers, and policymakers better address the issues and challenges of adapting evidence-based innovations in care transitions for older adults to local contexts.