If you want to go to Banff/Lake Louise, definitely consider going to the Calgary Stampede at the beginning of July. Be aware that Jasper National Park is a disaster in progress due to wildfires. According to the Alberta Premiere, 30-50% of the buildings in the town of Jasper have been damaged.
Personally, I would consider flying into Missoula or Bozeman MT or possibly Jackson, WY. From Bozeman, it is about 300 miles to Glacier, NP, 110 miles to Yellowstone NP and 180 miles to Grand Teton NP. These parks should all have moderate to cool temperatures in the summer. These destinations are all relatively expensive to fly to in the summer. It would be a good time to use airline miles. A couple of tips on airline award travel. Don't try to book airline awards round trip. There is no benefit to it. Book them as one ways. This allows you to more easily change flights if better pricing/times become available and allows you to mix dollars and miles. Don't have many miles?, it is easy to obtain them with credit cards. American currently has a deal with Barclays where you get 70k American miles with the first purchase on a new card.
If you are planning on staying in the national parks for next July, the best time to book hotels was
yesterday!! Seriously. These book up very far in advance. Also be aware that the hotels inside the national parks generally provide poor value for the money. Their main benefit is their location. For Yellowstone, their are several timeshares in West Yellowstone. Grand Teton NP is about 20 minutes from downtown Jackson, WY. Kalispell and Whitefish are close to the west side of Glacier NP. St Mary is close to the east side.
Another possible destination is Rocky Mountain NP west of Denver. There are plenty of timeshares to the southwest of the park and regular hotels to the east.
I would also suggest not picking up a rental car on a weekend day. Last summer, my wife and I flew into Denver in late June on a Saturday. The cupboard was almost bare. Had a reservation with Hertz (am President's club), had to wait for 45 minutes for a vehicle. Ended up driving a Jeep Compass for a month and it was a piece of crap. Other rental agencies were totally out of cars. Some of their buses were dropping their customers at the Hertz rental center!
For that trip, we visited Scotts Bluff, Black Hills of SD (including Mt Rushmore and Custer State Park), Minuteman Missile Sites, Badlands NP, Cody WY(7/4 Stampede), Yellowstone NP, Grand Teton NP, Jackson WY, Rocky Mtn NP and Breckenridge. Finally go to see the Red Rocks amphitheater near Denver; unfortunately not for a show.
Currently planning a trip for next summer. At the moment, itinerary looks like Western MT including Glacier NP>Waterton NP>Calgary (Stampede)>Banff(honeymooned here)>Jasper (we hope)>Kamloops>Victoria BC>Olympic NP>Rainier NP>Washington wine country>Jackson WY>Steamboat Springs, CO>Laramie, WY.
If you have questions, let me know.
Attaching a picture of the Grand Tetons.