Ashlu season is typically much later in summer, we usually start heading up there in august/september.
There will be stuff to run though. The Bridge river in Lillooet is a 16 mile IV run with some slow sections and some great sections of technical pool drop.
The Similkameeen is a big river III-IV that should be maching around that time.
I'm not up on the creek runs available at that time of year, but squamish
and lilloet ought to have many options in the IV-V range.
A place you might want to check for beta is the Back Eddy forums on the WKABC: WKABC Backeddy Forum