Bonus eligibility whilst off on approved leave – Ontario

Can you advise legally how to pay out a quarterly bonus to an employee who is on STD (so justified).  Do we pro-rate the payment as to the time they were working i.e. worked 1 of the 3 months?  And if not do we pay on total base comp i.e. 1 month full wage and 2 months of STD wage.
 
Thank you.