Planning a Train Trip to Canadian Rockies?

My husband and I will be celebrating 40 years on Valentine's Day. We would like to take a train trip to the Canadian Rockies sometime during the year, but not in February because of the cold and snow. What I'd like to know, if any of you have done this, is what is the best time of year to do this? And from where to where? Any advice, tips, or even warnings would be greatly appreciated. Thanks.

By Margaret from TX