What was found
(CAN) AFTER TAKEOFF FROM YUL LANDING GEAR LEVER WILL NOT MOVE UP. GEAR RETRACTED WITH LOCK TRIGGER OVERRIDE. REVERSER ISOLATION VALVE LIGHT ILLUMINATED IN FLIGHT. ON APPROACH TO YYZ LANDING GEAR POSITION LIGHTS NOT ON WHEN GEAR HANDLE SELECTED DOWN. VISUAL CHECK BY TOWER INDICATED GEARS WERE DOWN. CFR CALLED, LANDED WITHOUT FURTHER INCIDENT. AFTER LANDING UNABLE TO HAVE APU POWER 2ND BUS (1 OR 2) ON LINE. TROUBLESHOOTING FOUND LANDING GEAR LIGHTS CIRCUIT BREAKER OUT. REPLACED LANDING GEAR ACCESSORY UNIT AS PER WORK CARD 4286.