I'd say that it is impossible to simulate climbing on a trainer simply from a cardiovascular point of view.

Personally, my sustained heart rate on a trainer is always lower than when I am climbing (150 versus 170). I am not sure why but most likely due to a lack of form during the winter and maybe lack of willpower.

Anyways, trainers are not suppose to give a good cardio workout like climbing. The only good it can do is improve pedalling motion and strength. Intervals can also be done on the trainer, but usually there is no point in peaking during the winter.