Here are my inputs for Lac Memphremagog. I spend my summer weekends there on the lake, I know it well. Sorry for the english
Honestly if there is no South component in the wind its a bad place to kite. Prevailing wind is West which is far to gusty to enjoy, I have tried many many times in desperation. A good kite session is rare. Windsurfing is far better here. All of the west facing shoreline (east side of lake) is private, tree lined and too deep to water launch ( I have done it once at low water levels in the fall, very sketchy and still ended up with gusty wind). Launching in the park east of the pier is possible in off season for west wind, but prohibited during the summer, I have been given shit by City workers.
North wind, forget about it unless you have a boat to launch from. The mountain makes gusty wind. Boat launching in some of the south bays would be ok but shallow water is hard to find which makes it difficult.
The forecasts for Magog are also very tricky, getting SKUNKED is to be expected. Basically not worth traveling there unless you have a cottage there or a backup plan for the afternoon. Its a great winter spot, but summer is limited to south wind.