In the great book "How to win better positions", it was calculated that an advantage of about +1.50 is enough to win, provided both sides play PERFECTLY. If the evaluation is less than +1.50, it should be a draw if, once again, both sides play perfectly.
That being said, no one plays perfectly (not professionals, or beginners). However, it is safe to assume that professionals are much closer to this "perfect" level of play. So we only need to increase the +1.50 by a small amount. +1.80 to +2.00 should be enough to more or less guarantee a win for one of the sides in a match between two professionals.
However, there are other variables to take into account. If the position is simple and one side is up 2 clear pawns (giving a +2.00 advantage), then there is a +99% chance the professional will win. Conversly, if the position is very complex and one side is up 2 points just by the engine evaluation, then the outcome is not at all certain. The engine may evaluate a complex position to be +2.00, but for humans in a practical game it could seem equal to them.
For amateurs, we need to increase the margin far greater, since they are far from the margin of "perfect play". To guarantee a win for an amateur, one would probably need to provide at least a +3.00 advantage, due to the possibility of blunders and mistakes. Even at this level of an advantage though, it is not certain that an amateur will not make some game losing blunder.
For beginners, there is likely no advantage you can give that will ensure a win. Beginners make game losing blunders very frequently, which makes an engine evaluation more or less moot. There is no evaluation that would guarantee a win for beginners, due to the unpredictability of their skill.
To summarize, for top level professionals about a +2.00 advantage is needed to secure the win. For amateurs, you'd probably need at least a +3.00 advantage. For beginners, there is no number. For engines that play "perfectly", at least a +1.50 advantage is needed. However, it is important to keep in mind that it depends on the type of position too. Simple positions provide more certainty that the better side will win. Complex positions make the result far more uncertain.