Hi Everyone!
we would like to plan a road trip from Seattle to Banff and Jasper in, let’s say 19-28 of August.
I have little time for planning now, but I know I have to secure lodging (and maybe park tickets?). We are two adults and 3 kids (11,10,7). Good on long drives, and love to hike intermediate trails, see animals in nature, views, lakes, amusement parks etc
I would be GRATEFUL if you could offer specific lodging places that I could secure now while I keep planning.

what I have in mind now:

19: Leave Friday afternoon to cultus lake. Sleep around there (where ?).
20: Spend most day on Saturday in the water park or adventure park (is it worth it?). Sleep at Kamloops (where?)
21-22-23 Sleep and explore Banff abs Lake Louise area
23: stay at Rampart creek wilderness hostel (already reserved but can cancel)
24-25-26 explore Jasper
27- start driving home, sleep on the way
28- back in Seattle

Thank you so much for your help and advice!

Welcome to Fodors. Just a very quick comment right now. For almost the exact same drive time I'd do a big loop instead. Seattle > Spokane > Banff > Jasper > Kamloops > Seattle . . . so you'd see different country coming an going.

MY initial impulse based on what you've laid out would be to NOT pause at/near Cultus Lake for anything other than lodging overnight... and then expedite the journey to Alberta, where 3.5 hours east of Jasper you could take the gang to the West Edmonton Mall, where the water park is among the largest in North America... and where anyone who needs a break can know a vast assortment of nearby entertainment.

Maybe shave one day off of "Jasper" for that purpose.

Among other things, at the massive water park at the massive mall, your gang wouldn't be out in the sun all day, which probably wouldn't harm the cause.

Never been, but the Cultus bay waterpark looks good for kids your age. In Banff we’ve stayed three times at the High Country Inn with our kids. They have family rooms, right in town, breakfast, small indoor pool, not fancy but priced well. In Jasper our first choice has been Patricia Lake Bunglows, but last time they were booked and we stayed at Becker Chalets. Both are reasonable, have a variety of accommodations, Patricia Lake on a lake Becker on the river. Both a bit outside of town, but with kitchen facilities. Patricia Lake has canoes/kayaks/rowboats and firepits to enjoy after a day exploring/hiking that our kids enjoyed.