Yeah, i'd definitely use fresh. I feel like cashews would be too creamy and not really like the sauce i've had in restaurants. When I googled Chinese White Sauce, I found a bunch of recipes right away including this one: http://www.bargaineering.com/articles/c ... cipes.html
They use fresh ingredients and seemed to have some white wine in them, too. Mostly I remember these dishes being salty and garlicky.