We constrained APSIM-Canola model to 35 site-years phenology data of 10 cultivars. Cultivar parameters for anthesis & maturity derived with Bayesian optimisation. Critical photoperiod below which development slows down was found to be 20 h. Equifinality exists and can potentially lead to wrong cultivar characterisation. Quantification of vernalisation & photoperiod sensitivity can improve simulations.