C-GWEO, a de Havilland DHC-8-400 aircraft operated by WestJet Encore, was conducting flight WEN3504 from London (CYXU), ON to Toronto/Lester B. Pearson Intl (CYYZ), ON. During the approach at CYYZ, the crew selected flaps down and received a Flap Power Caution Light. A goaround was conducted and the QRH procedures were performed which eliminated the Caution Light. During the second approach the crew selected FLAP 10 and the Caution Light returned. The crew declared a PAN PAN and proceeded to perform an uneventful landing. ARFF were standing by for the landing and checked the brakes for overheating due to the higher than normal landing speed. Once cleared the aircraft taxied to the gate. Maintenance found a faulty pressure switch within the Flap Power Unit and replaced it.