first of all, all the results will have your starting date as the wetland layer initial date. So, for what concerns the SLR, the actual sea level increase is from the SLR scenario curve selected but only from the initial date of the model (2012 for you), e.g. if you select 1 m SLR scenario you will have 0 m SLR by 2012 and 0.8841 m SLR by 2100, calculated by rescaling A1B-Maximum (see Technical Documentation).
In your case, your actual SLR curve cannot be included at the moment. However, you can select custom scenarios for studying a scenario that has same overall SLR change by 2100 but uses A1B-max as base curve. As an example, if you want to see x=CanadaSLR2100-CanadaSLR2012 you have to input x/0.8841, e.g. if you want to study the case of 1 m SLR between 2012-2100, you have to input 1.131 m.
Hope it helps and good luck,