I've been there few times. It's hard to predict wind there.
Yes, if it's strong outflow in Howe Sound, then it should be windy. Last time it wasn't sunny day at Whistler and wind still was good. Also look for temp difference between Lillooet, Pemberton, Whistler, Vancouver, with opposite gradient that you want for summer Squamish.
Last time outflow was strong gusting to 40kn afternoon. On a lake was 20-25kn gusts, 5m was enough for me 70kg, on powder skis.
This meter show wind every 4h, last time it was around 10kn.
https://wx.ikitesurf.com/spot/95824