I'd have thought you'd be fine to come at that time. Everything is pumping right now with all the heat we've had and there's still a lot of snow left up top.
Obviously some rivers drop before others but I'd have thought you'd be good for Upper Cheak, Balls to the Wall and Callaghan.
Fear Canyon is a great option if other stuff gets a bit boney - we ran it last year in late October and it was still clean at a nice non-pushy class IV. Soo could also be good - very under rated run in my opinion.
Give me a shout nearer the time if you want for more info. or to hook up for a paddle.
Check out LiquidLore - British Columbia
Home - Real-time Hydrometric Data - Environment Canada
for water levels (look for Cheakamus river above Millar creek and Elaho river at mouth). Upper Cheak is runnable between 2.0 and over 3.0 but best between 2.4 and 2.7 IMO.
Also check out Whitewater Whistler on facebook for a bit of local knowledge and some pictures.