I just decided to go with my daughter to Banff and Jasper in early August. Lodging was a bit of an issue but nothing like in US parks where there's very little. I managed to get what I needed and still could make a slight change.

We're spending a total of 5 complete days and that includes a good part of one day in Yoho.

I did a lot last year in 2 1/2 days so 5 is a luxury.

I don't know how long you were planning on but you should do them together.

4 or 5 day. Still think I would like to do 4 days at each place.

With only 4 or 5 days, your best bet is to stay in Banff/Lake Louise and just drive part way up the Icefields Parkway on one of your full days.

Otherwise you will be very rushed, and not get to enjoy the scenery/sights. With four days, you could do one in the Banff townsite area, another on the Icefields, one in Yoho and have another to do Lake Louise/Moraine Lake/Johnston Canyon.