For late July from Kamloops, you may want to consider fishing the Thompson River. Less gear to carry and the fishing should be reasonably good, especially in the evening hours until dark.
Juniper Beach Provincial Park is a good spot to visit for day use area. Going either upstream or downstream from the day use area, or even in front of the campground, can be productive for rainbow trout. If you are fly fishing, get yourself a variety of large stonefly nymphs for fishing during the day, and dries for the evening hours. If you are spincasting, small Gibbs Croc spoons will get you fish on almost every cast at times, with a few northern pikeminnow mixed in between.
For lake fishing, consider heading to either Leighton Lake or Tunkwa Lake during that time of the year. The bomber hatch should be happening and fishing can be pretty good. Both lakes can get pretty windy in the afternoon, so just keep that in mind when being in a float tube. Here are a few videos of Leighton Lake from a few years ago.
http://www.youtube.com/watch?v=lm5GrAtbrTMhttp://www.youtube.com/watch?v=JE4VGqmmQnAhttp://www.youtube.com/watch?v=Hbv76umhuWELogan Lake is another one worth visiting, a smaller lake and probably more manageable from a float tube. Here is a video I just put up on fishing with Brian Chan there last August.
http://www.youtube.com/watch?v=TTMZfB6wDXo