Banff will be great during April. Its still possible to get great powder days in April. When you hit may Sunshine will still be good but Lake Louise will close in the first week of May so it could be a bit light on.
If its for your honeymoon I would check out the Chateau Lake Louise and the Banff Springs hotels. Both are amamzing places to stay!
The one good thing about April is that Sunshine will be guaranteed to have great conditions. Depending on when in April there is also opportunities for non ski activities like snow mobiling and dog sledding.
I live in Banff so if you have any questions let me know.