Understanding stress distribution and the impact of random field defects on the long-term integrity of bond-critical CFRP applications in critical civil infrastructure is vital for developing a comprehensive numerical and analytical model for performance-based design codes. This study examines the debonding mechanisms of carbon fibre-reinforced polymer (CFRP) sheets used to strengthen the recently deconstructed Champlain Bridge in Canada to assess bond strength and interfacial parameters under single and double shear loading conditions while considering various interfacial defects. To test the extracted elements from the bridge, a new shear-lap configuration was designed which did not require gripping of the FRP sheets. After the first phase of testing, the other ends of the blocks were retested in a conventional push-pull single-shear lap configuration. Finally, double shear lap tests were also conducted, for a total of 27 test results. The strain profiles and displacement were obtained using Digital Image Correlation and strain gauges, enabling a comprehensive analysis of the strain variation across the bond length for different test configurations. Results indicate that the double shear lap test generally resulted in more consistent peak loads. At the same time, the new single shear-lap setup yielded lower peak strains and greater variability in test results. The findings suggest that the newly designed shear-lap setup can produce reliable results in a double shear-lap configuration while out-of-plane rotation occurred when the same setup is employed for single shear-lap testing.