I'm new to that area but I've been watching it closely trying to figure it out.
If the wind is pushing south to north through Hope, Lytton, Ashcroft etc. then it is windy at Harrison.
Wind usually starts in early afternoon. Bear Creek wind kicks in an hour after wind at the breakwater. Bear Creek wind is 5kts stronger.
On July 10 I was there. I'd rather be fully lit on the water rather than struggling with smaller kite to stay upwind. On this day I was on 12M with twin tip and was fully lit. Not overpowered but I think I could've downsized and been fine. Everyone else was out on 9's and 10's and they were doing just fine. My point is sometimes the Ikitesurf graph shows wind that appears to be light when in fact on the water the wind is stronger. (my opinion)
I've only kited bear creek and breakwater once. Wind at both locations was very steady with no lulls, or crazy gusts. The wind coming over the breakwater can be swirly, but most people just launch and go out into the lake.
No rescue services, but if other kiters are there, you will be fine, just say hello so they know you're new. Bear creek is awesome. Nice waves and scenery but without a boat or other kiters there I would not go out alone. It's kind of spooky because the next bail out spot is 7 km down the lake.
http://harrisonwindsports.com/?page_id=664