A 2008 paper looked into this very worst-case scenario, the most massive slide that could happen (though unlikely and probably impossible right now with the present day geology). They find wave heights in the range 10 to 188 meters in the Canary Isles themselves. But the waves interfere and dissipate as they head out into the Atlantic. They predict 40 meters height for some nearby island systems. For continents, the worst effects are in Northern Brazil (13.6 m), French Guyana (12.7 m), mid-US (9.6 m), Western Sahara (largest prediction at 37 meters) and Mauritania (9.7 m). This is not large enough to count as a megatsunami, with the highest prediction for Western Sahara comparable to the Japanese tsunami, so it would only be a megatsunami locally in the mid Atlantic.