A few thoughts, starting with the fact that there are at least several threads discussing trips to YNP and GTNP. In case you have not found those, search some more.
I respectfully disagree with Pioneer with respect to a side trip to Glacier for your trip: it is a likely a full day to drive there and another to drive back; for an eight day trip, you would lose too much time. Do Glacier and Waterton NPs on a different trip; they would also fill up a full week+.

IIRC, Canyon Lodge is far below both the (Old Faithful?) Snow Lodge and Jackson Lake Lodge, just so your expectations are realistic.
Are you flying and if so, into where? JAC, BZN, CDY, etc.? In July, YNP roads may be packed and slow so that travel times may be much longer than they appear on the map. For an 8 day trip, I think a ratio of 5 YNP/3GTNP is pretty good. I probably would use a portion of one of the GTNP days to go into Jackson instead of using a YNP day to go to Cody.
There are a number of good books on day/short hikes in YNP. There are a lot more such hikes in YNP than GTNP, in my experience.
Around GTNP and Jackson, assuming good water flow, you should have opportunities for float trips (Class I) or rafting trips (Class II+). I would recommend looking into these.
Enjoy!