Lake Louise

The Canadian Rockies area of Lake Louise, Banff and Jasper are best done in the Summer.
We did it in late August and it was fantastic.
We had a four day tour from Vancouver with a company called Key West.

As a Canadian, we often see these destinations differently, so I find it difficult to know how many days to recommend. It is expensive. I also think September into early October could be lovely with changing leaves. It won't change the prices, but may change some of the tourist numbers.
The Icefield Parkway to Jasper is also worth traveling, and I am pretty sure it can be done as a day trip, if you aren't driving. Parking is a nightmare in Banff.
I would think 3 days at a minimum. 5 would be better is doing the Icefield Parkway.

I agree with MariaF. Five full days at a minimum and if you can add a couple of more, spend time in Jasper which is much more scenic than Banff. The Maligne Canyon in Jasper is lovely. Get to Lake Louise as early as possible. Parking is difficult and depending on the time of year you may need to shuttle. Plenty of walks and hikes around the lake. The Icefields Parkway linking Banff and Jasper is a must and there is hiking at any number of places along the Parkway. Stop at Peyto Lake, my favorite.

• When are you going?
• By "Banff" do you mean the Town of Banff or Banff National Park?
• The Town of Banff and Lake Louise could be a daytrip but to experience the region I'd take at least a week and do what others have suggested. The Icefields Parkway is one of the most scenic drives in the world. I'd consider a few days in Jasper as well after driving the Parkway.
• if Lake Louise is on the itinerary then you need to plan ahead and book a shuttle in advance, parking is usually full in the summer by 7am and vehicles are no longer allowed in Moraine Lake. https://parks.canada.ca/pn-np/ab/banff/visit/parkbus/louise
• Hotel prices in Banff and Canmore are obscene this year, I'd advise an early to mid-September trip when weather is still nice but tourist season is slowing and hopefully hotel prices will become more reasonable again.

We stayed 3 in Banff, 3 in Lake Louise, and 3 in Jasper in September of 2018. Our longest/most difficult hike was Lake Agnes Teahouse. I thought the number of days was perfect for us.

Allan speaks truth. Todays TV news showed the newish restrictions on the shuttle, which are expected to really factor in come August.
Agree that fall is a wonderful time.
Tip: maybe check out reserving a visit up to Lk. O'Hara.
I am done. the canux

I would say a minimum of 5 days, but 7 would be better. We first visited these areas on our honeymoon 33 years ago and we kept going back. The first time we had 10 days which was ideal. The other times we had about a week and that was doable, as we knew we would return. If this is a one time trip there though, try to give yourself a full week.