Obviously I cannot recreate an entire college level textbook here, so I will have to assume that you have seen some of this before.
As a first guess, I might suggest that you see if Raoult's law is adequate for your purposes:
P(tot)=total pressure
P(H2O)=Partial pressure of water
x(H2O)=mole fraction water in the liquid phase
P0(H2O)=vapor pressure of pure water at T.
P(tot)=P(H2O)=x(H2O)*P0(H2O)
Note that we are assuming that the sugar is completely non-volatile, which should be a good assumption at low temperatures, but may be a poor assumption if the temperature gets high enough. Also note that concentration is in mole fraction, so you may need to convert whatever your concentration units are to mole fraction. At this point, I will assume that you have seen this sort of thing before and know how to solve this equation for "boiling point temperature".
As a second guess, I might suggest a simple "modified Raoult's law", where we assume the vapor phase is ideal and we can model the non-idealities in the liquid with a simple activity coefficient:
gamma(H2O)=activity coefficient of water
P(tot)=P(H2O)=x(H2O)*gamma(H2O)*P0(H2O).
I don't know how Aspen will prefer to have this done. It is certainly possible to solve this equation for gamma(H2O), then fit those activity coefficients to your desire activity coefficient equation. Some algorithms will take the P, T, and x data and a chosen activity coefficient model and regress on boiling point directly using the parameters of the activity coefficient model.